PHY 1410 Topics Study Help (not created by me)

A driver drives for 3.7 hours at an average speed of 53 MPH. What distance does she travel in this time?

196.1 mi 2-3

A ball traveling in a circle with a constant speed of 12 m/s has a centripetal acceleration of 4 m/s2. What is the radius of the circle?

36 m 5-5

At a given instant in time, a 3-kg rock is observed to be falling with an acceleration of 6.0 m/s2. What is the magnitude of the force of air resistance acting upon the rock at this instant? (Use g = 10 m/s2.)

12 N 4-16

A weight of 15 N is located at a distance of 16 cm from the fulcrum of a simple balance beam. At what distance from the fulcrum should a weight of 20 N be placed on the opposite side in order to balance the system?

12 cm 8-10

A car moving with an initial velocity of 12 m/s slows down at a constant rate of −5 m/s2. What distance does the car cover in this time?

13.5 m 2-12b

Suppose that the gravitational acceleration on a certain planet is only 2.9 m/s2. A space explorer standing on this planet throws a ball straight upward with an initial velocity of 30 m/s. What is the velocity of the ball 4 seconds after it is thrown?

18.4 m/s 3-16a

A steel ball is dropped from a diving platform (with an initial velocity of zero). Use the approximate value of g = 10 m/s2. What is the velocity of the ball 2.0 seconds after its release?

20 m/s 3-8a

A ball is thrown downward with an initial velocity of 12 m/s. Using the approximate value of g = 10 m/s2, what is the velocity of the ball 1.5 seconds after it is released?

27 m/s 3-10

A person in a hurry averages 55 MPH on a trip covering a distance of 211 miles. What time was required to travel that distance?

3.8 hr 2-4

A runner traveling with an initial velocity of 1.7 m/s accelerates at a constant rate of 1.2 m/s2 for a time of 6 seconds. What distance does the runner cover during this process?

31.8 m 2-11b

What is the weight of a 35-kg mass?

343 N 4-10

A 0.20-kg ball traveling with a speed of 22 m/s is brought to rest in a catcher's mitt. What is the size of the impulse exerted by the mitt on the ball?

4.4 kg m/s 7-5

A rocket ship at rest in space gives a short blast of its engine, firing 22 kg of exhaust gas out the back end with an average velocity of 196 m/s. What is the change in momentum of the rocket during this blast?

4312 kg m/s 7-12

A steel ball is dropped from a diving platform (with an initial velocity of zero). Use the approximate value of g = 10 m/s2. How far does it fall in the first 3 seconds of its flight?

45 m 3-9b

A ball rolls off a table with a horizontal velocity of 3 m/s. Assume it takes 0.5 seconds for it to reach the floor. What is the vertical component of the ball's velocity just before it hits the floor? (Use g = 10 m/s2.)

5 m/s 3-21a

A hiker walks with an average speed of 1.5 m/s. What distance in kilometers does the hiker travel in a time of 1 hour?

5.4 km 2-5

A ball is dropped from a high building. Using the approximate value of g = 10 m/s2, find the change in velocity between the second and seventh second of its flight.

50 m/s 3-11

A ball is traveling at a constant speed of 5 m/s in a circle with a radius of 0.5 m. What is the magnitude of the centripetal acceleration of the ball?

50 m/s2 5-4

What is the mass of a 485-N weight?

50.51 kg 4-11

A roller-coaster car has a potential energy of 468 000 J and a kinetic energy of 128 400 J at point A in its travel. At the low point of the ride, the potential energy is zero, and 53 000 J of work have been done against friction since it left point A. What is the kinetic energy of the roller coaster at this low point?

543400 J 6-21

A steel ball is dropped from a diving platform (with an initial velocity of zero). Use the approximate value of g = 10 m/s2. Through what distance does the ball fall in the first 1.1 seconds of its flight?

6.05 m 3-9a

A projectile is fired at an angle such that the vertical component of its velocity and the horizontal component of its velocity are both equal to 25 m/s. What horizontal distance does the ball travel in this time?

62.5 m 3-24b

The acceleration of gravity on the surface of Jupiter is 26.7 m/s2. What is the weight on Jupiter of a woman whose weight on Earth is 240 lb?

654 lb 5-19

A student, sitting on a stool rotating at a rate of 40 RPM, holds masses in each hand. When his arms are extended, the total rotational inertia of the system is 7.5 kg · m2. He pulls his arms in close to his body, reducing the total rotational inertia to 4.5 kg · m2. If there are no external torques, what is the new rotational velocity of the system?

66.67 RPM 8-18

A ball is thrown upward with an initial velocity of 14 m/s. Using the approximate value of g = 10 m/s2, what are the magnitude and direction of the ball's velocity 2.10 s after it is thrown?

7 m/s downward 3-14b

A ball is thrown upward with an initial velocity of 14 m/s. Using the approximate value of g = 10 m/s2, how high above the ground is the ball 2.00 s after it is thrown?

8 m 3-15b

A runner traveling with an initial velocity of 1.7 m/s accelerates at a constant rate of 1.2 m/s2 for a time of 6 seconds. What is his velocity at the end of this time?

8.9 m/s 2-11a

A ball is thrown upward with an initial velocity of 14 m/s. Using the approximate value of g = 10 m/s2, how high above the ground is the ball 1.00 s after it is thrown?

9 m 3-15a

Is it possible for two objects with the same mass to have different rotational inertias? Explain. a. Yes, if the two objects of the same mass are rotating with different angular velocities then they will have different rotational inertias. b. Yes, if the same mass is distributed at different distances from the axis of rotation in the two cases. c. No, two objects with the same mass will always have the same rotational inertia because only the total mass not the distribution of mass determines the rotational inertia.

b. Yes, if the same mass is distributed at different distances from the axis of rotation in the two cases. 8-12

Is the principle of conservation of momentum always valid, or are there special conditions necessary for it to be valid? a. Momentum is always conserved for any system. b. Momentum is conserved for any system when the total change in momentum is not equal to zero. c. Momentum is conserved for any system when a constant nonzero force is acting on the system. d. Momentum is conserved for any system when the net force acting on the system is equal to zero.

d. Momentum is conserved for any system when the net force acting on the system is equal to zero. 7-7

During what phase of the moon can a solar eclipse occur? a. Full moon b. Half moon c. During any phase d. New moon

d. New moon 5-20

The rotational velocity of a merry-go-round increases at a constant rate from 0.6 rad/s to 1.5 rad/s in a time of 10 s. What is the magnitude of the rotational acceleration of the merry-go-round?

.09 rad/s2 8-5

A 0.06-kg ball moving in a circle at the end of a string has a centripetal acceleration of 4 m/s2. What is the magnitude of the centripetal force exerted by the string on the ball to produce this acceleration?

.24 N 5-6

A spring with a spring constant k of 18 N/m is stretched a distance of 24 cm (0.24 m) from its original unstretched position. What is the increase in potential energy of the spring?

.52 J 6-15

A car travels with an average speed of 28 m/s. what is this speed in km/h?

100.8 2-6b

If a world-class sprinter ran a distance of 100 meters starting at his top speed of 9 m/s and running with constant speed throughout, how long would it take him to cover the distance?

11.11 s 2-13

A projectile is fired at an angle such that the vertical component of its velocity and the horizontal component of its velocity are both equal to 25 m/s. Using the approximate value of g = 10 m/s2, how long does it take for the ball to reach its high point?

2.5 s 3-24a

A net force of 42 N acting on a wooden block produces an acceleration of 1.5 m/s2 for the block. What is the mass of the block?

28 kg 4-4

A ball rolls off a table with a horizontal velocity of 3 m/s. Assume it takes 0.5 seconds for it to reach the floor. What is the horizontal component of the ball's velocity just before it hits the floor? (Use g = 10 m/s2.)

3 m/s 3-21b

A ball is thrown upward with an initial velocity of 14 m/s. Using the approximate value of g = 10 m/s2, what are the magnitude and direction of the ball's velocity 1.05 s after it is thrown?

3.5 m/s upward 3-14a

Suppose that a merry-go-round is rotating at the rate of 15 rev/min. a. Express this rotational velocity in rev/s. b. Express this rotational velocity in rad/s.

a. .25 rev/s b. 1.57 rad/s 8-3

An ice skater with a mass of 85 kg pushes off against a second skater with a mass of 33 kg. Both skaters are initially at rest. a. What is the total momentum of the system after they push off? b. If the larger skater moves off with a speed of 1.8 m/s, what is the corresponding speed of the smaller skater?

a. 0 kg m/s b. 4.64 m/s 7-11

At the low point in its swing, a pendulum bob with a mass of 0.2 kg has a velocity of 13 m/s. a. What is its kinetic energy at the low point? b. Ignoring air resistance, how high will the bob swing above the low point before reversing direction?

a. 16.9 J b. 8.6 m 6-19

Suppose that a disk rotates through three revolutions in 3 seconds. a. What is its displacement in radians in this time? b. What is its average rotational velocity in rad/s?

a. 18.84 rad b. 6.28 8-4

Two forces are applied to a merry-go-round with a radius of 2.5 m, as shown in the diagram below. One force has a magnitude of F1 = 74 N and the other a magnitude of F2 = 58 N. ^ | F1 | <--F2--O a. What is the torque about the axle of the merry-go-round due to the 74-N force? b. What is the torque about the axle due to the 58-N force? c. What is the net torque acting on the merry-go-round?

a. 185 Nm counterclockwise b. 145 Nm clockwise c. 40 Nm counterclockwise 8-11

A pendulum swings through 10 cycles in 5 seconds. The frequency of the pendulum is: a. 2 Hz. b. 10 Hz. c. 0.1 Hz. d. 0.5 Hz. e. 5 Hz.

a. 2 Hz. 6-23

A sled and rider with a combined mass of 85 kg are at the top of a hill a height of 30 m above the level ground below. The sled is given a push providing an initial kinetic energy at the top of the hill of 1200 J. a. Choosing a reference level at the bottom of the hill, what is the potential energy of the sled and rider at the top of the hill? b. After the push, what is the total mechanical energy of the sled and rider at the top of the hill? c. If friction can be ignored, what will be the kinetic energy of the sled and rider at the bottom of the hill?

a. 24990 b. 26190 c. 26190 6-20

A force of F = 19 N is applied at the end of a wrench handle that is L = 40 cm long. The force is applied in a direction perpendicular to the handle. a. What is the torque applied to the nut by the wrench? b. What would the torque be if the force were applied halfway up the handle instead of at the end?

a. 7.6 Nm b. 3.8 Nm 8-9

A railroad car with a mass of 16 000 kg collides and couples with a second car of mass 15 000 kg that is initially at rest. The first car is moving with a speed of 6 m/s prior to the collision. a. What is the magnitude of the initial momentum of the first car? b. If external forces can be ignored, what is the magnitude of the final velocity of the two railroad cars after they couple?

a. 96,000 kg m/s b. 3.09 m/s 7-16

Suppose an astronaut in outer space suddenly discovers that the tether connecting her to the space shuttle is cut and she is slowly drifting away from the shuttle. Assuming that she is wearing a tool belt holding several wrenches, how can she move herself back toward the shuttle? Explain. a. She can throw the wrenches very rapidly in the same direction she is moving in order to change her momentum's direction. b. She can disconnect the tool belt so that her mass density will decrease, resulting in a smaller acceleration due to gravity. c. She can hold the wrenches outward so the radiation pressure of the cosmic wind will push her in the direction of the shuttle. d. She can throw the wrenches toward the shuttle very rapidly in order to propel herself in the direction of the shuttle. She can tie the wrenches to the end of the tether and spin the tether like a propeller.

a. She can throw the wrenches very rapidly in the same direction she is moving in order to change her momentum's direction. 7-13

Suppose that a mass is hanging vertically at the end of a spring. The mass is pulled downward and released to set it into oscillation. Is the potential energy of the system increased or decreased when the mass is lowered? Explain. a. The elastic potential energy of the spring increases the net potential energy of the system since the force stretching the spring is greater than the weight of the object. b. The net potential energy of the system decreases since the mass is lowered as the spring is stretched downward. c. The elastic potential energy of the spring decreases the net potential energy of the system since the force stretching the spring is less than the weight of the object. d. The net potential energy of the system remains the same since elastic potential energy increases while the gravitational potential energy decreases.

a. The elastic potential energy of the spring increases the net potential energy of the system since the force stretching the spring is greater than the weight of the object. 6-22

Two forces produce equal impulses, but the second force acts for a time twice that of the first force. Which force, if either, is larger? Explain. a. The first force is the larger force because it acts for a shorter amount of time. b. The second force is the larger force because it acts for a longer amount of time. c. The forces must be equal because their impulses are equal. d. There is not enough information to determine which force is greater.

a. The first force is the larger force because it acts for a shorter amount of time. 7-1

A pendulum is pulled back from its equilibrium (center) position and released. At what points in the motion of the pendulum after release is its kinetic energy the greatest? Explain. a. The kinetic energy is greatest at the center of the motion. b. The kinetic energy is greatest at the highest point of its motion. c. The kinetic energy is greatest at the midpoint between its center and highest point when the kinetic energy is equal to the potential energy.

a. The kinetic energy is greatest at the center of the motion. 6-16b

A skateboarder jumps on a moving skateboard from the side. Does the skateboard slow down or speed up in this process? Explain, using conservation of momentum. a. The skateboard slows down. Since more mass is added to the system, a compensating decrease in velocity must occur. b. The skateboard speeds up. Since more mass is added to the system, a compensating increase in velocity must occur. c. The skateboard neither slows down nor speeds up, since the initial velocity of the skateboarder is zero.

a. The skateboard slows down. Since more mass is added to the system, a compensating decrease in velocity must occur. 7-14

A pendulum is pulled back from its equilibrium (center) position and released. What form of energy is added to the system prior to its release? Explain. a. The work in raising the pendulum bob has gone into gravitational potential energy. b. No energy is added to the system prior to its release. c. The work in raising the pendulum bob has gone into kinetic energy.

a. The work in raising the pendulum bob has gone into gravitational potential energy. 6-16a

Is it possible for a baseball to have as large a momentum as a much more massive bowling ball? Explain. a. Yes, a fast baseball could possess the same momentum as a slow bowling ball. b. No, the bowling ball will have a greater momentum because its acceleration will always be less than the baseball. c. No, the bowling ball is much more massive so it will always have a larger momentum.

a. Yes, a fast baseball could possess the same momentum as a slow bowling ball. 7-2

Is there an advantage to following through when hitting a baseball with a bat, thereby maintaining longer contact between the bat and the ball? Explain. a. Yes, by following through the bat can remain in contact with the ball longer and yield a larger impulse. b. No, the force exerted on the ball by the bat determines the acceleration of the baseball and the distance that it will travel. c. No, there is no advantage to following through when hitting a baseball other than providing a smaller net force back on the arms of the player.

a. Yes, by following through the bat can remain in contact with the ball longer and yield a larger impulse. 7-3

When a cannon rigidly mounted on a large boat is fired, is momentum conserved? a. Yes, the total momentum of the boat, gun, and shell is zero both before and after firing since the forward momentum of the shell is equal to the recoil of the boat and gun. b. No, the total momentum of the boat, gun, and shell is zero before firing but the boat and gun have a nonzero momentum after the shell is fired. c. No, the total momentum of the boat, gun, and shell is zero before firing but after the firing the shell has a high velocity while the gun and boat have little or no velocity.

a. Yes, the total momentum of the boat, gun, and shell is zero both before and after firing since the forward momentum of the shell is equal to the recoil of the boat and gun. 7-10

Is the rotational velocity of a child sitting near the center of a rotating merry-go-round the same as that of another child sitting near the edge of the same merry-go-round? Explain. a. Yes, their rotational velocities are equal because all parts along a given line from center to edge are rotating at exactly the same rotational velocity. b. No, the child near the center has a higher rotational velocity since her radius from the center of motion is smaller and her angular displacement is smaller. c. No, the child near the edge has a higher rotational velocity since her radius from the center of motion is larger and her angular displacement is larger. d. There is not enough information to determine whether the children have the same rotational velocity.

a. Yes, their rotational velocities are equal because all parts along a given line from center to edge are rotating at exactly the same rotational velocity. 8-1

A fullback with a mass of 70 kg and a velocity of 2.0 m/s due west collides head-on with a defensive back with a mass of 88 kg and a velocity of 6.0 m/s due east. (Take the positive direction to be to the west.) a. What is the initial momentum of each player? b. What is the total momentum of the system before the collision? c. If they stick together and external forces can be ignored, what direction will they be traveling immediately after they collide?

a. full back = 140 kg m/s defensive back = -528 kg m/s b. -388 kg m/s c. east 7-8

A solid sphere and a hollow sphere made from different materials have the same mass and the same radius. Which of these two objects, if either, will have the greater rotational inertia about an axis through its center? a. hollow sphere b. solid sphere c. The rotational inertia of both spheres is the same since they have the same mass.

a. hollow sphere 8-13

A bowling ball has a mass of 6 kg and a speed of 0.75 m/s. A baseball has a mass of 0.12 kg and a speed of 28 m/s. Which ball has the larger momentum? a. momentum of the bowling ball b. momentum of the baseball c. neither

a. momentum of the bowling ball 7-4

A 4400-kg truck traveling with a velocity of 13 m/s due north collides head-on with a 1450-kg car traveling with a velocity of 22 m/s due south. The two vehicles stick together after the collision. a. What is the momentum of each vehicle prior to the collision? b. What are the size and direction of the total momentum of the two vehicles after they collide?

a. truck magnitude = 57,200 kg m/s north car magnitude = 31,900 kg m/s south b. 25,300 kg m/s north 7-17

Is angular momentum always conserved? Explain. a. Yes, angular momentum is always conserved for any system. b. No, angular momentum is only conserved when there is no net torque. c. No, angular momentum is only conserved when the angular acceleration is constant.

b. No, angular momentum is only conserved when there is no net torque. 8-14

A solid plank with a uniform distribution of mass along its length rests on a platform with one end of the plank protruding over the edge. How far out can we push the plank before it tips? Explain. a. None of the plank can protrude over the edge without resulting in a net torque. b. The plank can be pushed to its center point where the center of gravity is located without resulting in a net torque. c. Only about a third of the plank can hang over the edge before this mass results in a net torque. d. About two-thirds of the plank can protrude over the edge without resulting in a net torque.

b. The plank can be pushed to its center point where the center of gravity is located without resulting in a net torque. 8-8

Is it possible to balance two objects of different weights on the beam of a simple balance resting upon a fulcrum? Explain. a. Yes, it is possible if the respective distances (lever arms) from the fulcrum are chosen properly so that the larger weight has a larger lever arm. b. Yes, it is possible if the respective distances (lever arms) from the fulcrum are chosen properly so that the smaller weight has a larger lever arm. c. No, it is not possible to balance two different weights on the beam of a simple balance because the larger mass will always provide the larger torque.

b. Yes, it is possible if the respective distances (lever arms) from the fulcrum are chosen properly so that the smaller weight has a larger lever arm. 8-7

A grandfather clock that is regulated by a pendulum is taken to the Moon where the acceleration of gravity is less. Compared to an identical clock on Earth, the grandfather clock on the Moon will: a. keep time at the same rate. b. run slow. c. run fast.

b. run slow. 6-24

If momentum is conserved in a collision, does this indicate conclusively that the collision is elastic? Explain. a. Yes, momentum is conserved only in an elastic collision. b. No, momentum is conserved only in inelastic collisions. c. No, momentum is conserved in all collisions, elastic or inelastic.

c. No, momentum is conserved in all collisions, elastic or inelastic. 7-15

Is the linear speed of a child sitting near the center of a rotating merry-go-round the same as that of another child sitting near the edge of the same merry-go-round? Explain. a. Yes, their linear velocities are equal because all parts along a given line from center to edge are rotating at exactly the same linear velocity. b. No, the child near the center has a larger linear velocity because her radius is smaller and her rotational displacement is larger. c. No, the child near the edge has a larger linear velocity because her radius is larger while her rotational displacement is the same as the other child. d. Neither child has a linear velocity because they only have rotational velocity.

c. No, the child near the edge has a larger linear velocity because her radius is larger while her rotational displacement is the same as the other child. 8-2

A mass attached to a spring, which in turn is attached to a wall, is free to move on a friction-free horizontal surface. The mass is pulled back and then released. Suppose that the mass is halfway between one of the extreme points of its motion and the center point. In this position, is the energy of the system kinetic energy, potential energy, or a combination of these forms? a. The energy of the system is kinetic energy only. b. The energy of the system is potential energy only. c. The energy of the system consists of a combination of kinetic and potential energies. d. The system has no energy.

c. The energy of the system consists of a combination of kinetic and potential energies. 6-18

Two shotguns are identical in every respect (including the size of shell fired) except that one has twice the mass of the other. Which gun will tend to recoil with greater velocity when fired? Explain. a. The heavier gun will recoil faster since it has more mass and a larger velocity. b. Both shotguns will possess the same momentum upon recoiling, so they will recoil with the same velocity. c. The lighter gun will recoil faster since it has less mass and a larger velocity.

c. The lighter gun will recoil faster since it has less mass and a larger velocity. 7-9

A pendulum is pulled back from its equilibrium (center) position and released. At what points is the potential energy the greatest? Explain. a. The potential energy is greatest at the midpoint between its center and highest point when the potential energy is equal to the kinetic energy. b. The potential energy is greatest at the center of the motion. c. The potential energy is greatest at the highest point of its motion.

c. The potential energy is greatest at the highest point of its motion. 6-16c

A child on a freely rotating merry-go-round moves from near the center to the edge. Will the rotational velocity of the merry-go-round increase, decrease, or not change at all? Explain. a. The rotational velocity will not change because there is no change in the mass or the angular momentum of the merry-go-round. b. The rotational velocity must increase to conserve angular momentum because the rotational inertia of the merry-go-round will be less with the child near the edge. c. The rotational velocity must decrease to conserve angular momentum because the rotational inertia of the merry-go-round will be greater with the child near the edge.

c. The rotational velocity must decrease to conserve angular momentum because the rotational inertia of the merry-go-round will be greater with the child near the edge. 8-15

Moving straight inward, a large child jumps onto a freely rotating merry-go-round. What effect will this have on the rotational velocity of the merry-go-round? Explain. a. The rotational velocity must increase to conserve angular momentum once the mass is increased by the mass of the child. b. The rotational velocity will not change because there is no change to the angular momentum of the merry-go-round even with the addition of the child's mass. c. The rotational velocity must decrease to conserve angular momentum once the mass is increased by the mass of the child.

c. The rotational velocity must decrease to conserve angular momentum once the mass is increased by the mass of the child. 8-16

A pendulum is pulled back from its equilibrium (center) position and then released. When the pendulum bob is halfway between the high point and the low point in its swing, is the total energy kinetic energy, potential energy, or both? Explain. a. The total energy is kinetic energy only. b. The total energy is potential energy only. c. The total energy consists of half the original potential energy and half of the original potential energy converted to kinetic energy. d. The total energy consists of one-fourth the original potential energy and three-fourths of the original potential energy converted to kinetic energy.

c. The total energy consists of half the original potential energy and half of the original potential energy converted to kinetic energy. 6-17

A truck and a bicycle are moving side by side with the same velocity. Which, if either, will require the larger impulse to bring it to a halt? Explain. a. The truck and the bicycle will require the same impulse to stop them because they start at the same velocity and are stopped in the same distance. b. The bicycle will require a larger impulse to stop it because it has a smaller mass and can be stopped in a shorter distance. c. The truck will require the larger impulse to stop it because its larger mass gives it the greater momentum change.

c. The truck will require the larger impulse to stop it because its larger mass gives it the greater momentum change. 7-6

The diagram below shows the positions at intervals of 0.05 seconds of two balls moving from left to right. Are either or both of these balls accelerated? A --O-O-O--O--O--O---O---O----O-- B --O----O---O---O--O--O--O-O-O-- a. Neither ball is being accelerated. b. Only ball A is being accelerated. c. Only ball B is being accelerated. d. Both balls are being accelerated.

d. Both balls are being accelerated. 3-1

A car moving with an initial velocity of 12 m/s slows down at a constant rate of −5 m/s2. What is its velocity after 3 seconds of deceleration? (Indicate the direction with the sign of your answer.)

-3 m/s 2-12a

Two 250-kg masses (556 lb) are separated by a distance of 3 m. Using Newton's law of gravitation, find the magnitude of the gravitational force exerted by one mass on the other.

.000000463 N 5-17

A car travels with an average speed of 28 m/s. What is this speed in km/s?

.028 km/s 2-6a

A ball rolls off a shelf with a horizontal velocity of 3 m/s. At what horizontal distance from the shelf does the ball land if it takes 0.4 s to reach the floor?

1.2 m 3-19

A ball rolls off a table with a horizontal velocity of 4 m/s. If it takes 0.6 seconds for the ball to reach the floor, how high above the floor is the tabletop? (Use g = 10 m/s2).

1.8 m 3-20

Suppose that the gravitational acceleration on a certain planet is only 2.9 m/s2. A space explorer standing on this planet throws a ball straight upward with an initial velocity of 30 m/s. How much time elapses before the ball reaches the high point in its flight?

10.34 s 3-16b

The acceleration of gravity at the surface of the moon is approximately 1/6 that at the surface of the Earth (9.8 m/s2). What is the weight of an astronaut standing on the moon whose weight on Earth is 170 lb?

28.3 lb 5-18

A steel ball is dropped from a diving platform (with an initial velocity of zero). Use the approximate value of g = 10 m/s2. What is its velocity 3.9 seconds after its release?

39 m/s 3-8b

A 6.0-kg block being pulled across a table by a horizontal force of 35 N also experiences a frictional force of 10 N. What is the acceleration of the block?

4.17 m/s2 4-5

A horizontally directed force of 22 N is used to pull a box a distance of 3.2 m across a tabletop. How much work is done by the 22 N-force?

70.4 J 6-5

A Ferris wheel at a carnival has a radius of 16 m and turns so that the speed of the riders is 12 m/s. What is the magnitude of the centripetal acceleration of the riders? What is the magnitude of the net force is required to produce this centripetal acceleration for a rider with a mass of 80 kg?

9 m/s2 720 N 5-7

A force of F = 75 N is used to drag a crate d = 2 m across a floor. The force is directed at an angle upward from the crate so that the vertical component of the force is Fv = 45 N and the horizontal component is Fh = 60 N as shown in the diagram. a. What is the work done by the horizontal component of the force? b. What is the work done by the vertical component of the force? c. What is the total work done by the 75-N force?

a. 120 b. 0 c. 120 6-6

A net force of 20 N accelerates a 5-kg mass over a distance of 6 m. a. What is the work done by this net force? b. What is the increase in kinetic energy of the mass?

a. 120 J b. 120 J 6-9

A box with a mass of 4 kg is lifted (without acceleration) through a height of 6.0 m in order to place it upon the shelf of a closet. a. What is the increase in potential energy of the box? b. How much work was required to lift the box to this position?

a. 235.2 J b. 235.2 J 6-13

A 0.3-kg ball has a velocity of 16 m/s. a. What is the kinetic energy of the ball? b. How much work would be required to stop the ball?

a. 38.4 J b. 38.4 J 6-10

Jennifer has a weight of 125 lb. a. What is her weight in newtons? (1 lb = 4.45 N) b. What is her mass in kilograms?

a. 556.25 N b. 56.76 4-12

A lead ball and an aluminum ball, each 1 in. in diameter, are released simultaneously and allowed to fall to the ground. Due to its greater density, the lead ball has a substantially larger mass than the aluminum ball. Which of these balls, if either, has the greater acceleration due to gravity? Explain. a. Both will fall with the same acceleration, regardless of their mass. b. The lead ball will fall with greater acceleration because of its greater mass. c. The aluminum ball will fall with greater acceleration because of its small density.

a. Both will fall with the same acceleration, regardless of their mass. 3-2

Two masses are separated by a distance r. If this distance is doubled, is the force of interaction between the two masses doubled, halved, or changed by some other amount? Explain. a. Doubling the distance between them will result in 1/4 of the original force acting between them. b. Doubling the distance between them will result in half of the original force acting between them. c. Doubling the distance between them will result in doubling the original force acting between them. d. Doubling the distance between them will result in 4 times the original force acting between them.

a. Doubling the distance between them will result in 1/4 of the original force acting between them. 5-16

A rock is dropped from the top of a diving platform into the swimming pool below. Will the distance traveled by the rock in a 0.1-second interval near the top of its flight be the same as the distance covered in a 0.1-second interval just before it hits the water? Explain. a. No, the distance traveled in the 0.1 s just before hitting the water will be greater since the rock's velocity will be greater. b. No, the distance traveled in the first 0.1 s will be greater since the rock's velocity will be smaller. c. Yes, the distance traveled for any 0.1-s interval is the same since the rock's acceleration is constant. d. Yes, the distance traveled in the 0.1 s just before hitting the water will be the same since the rock is a projectile.

a. No, the distance traveled in the 0.1 s just before hitting the water will be greater since the rock's velocity will be greater. 3-6

Two identical pieces of paper, one crumpled into a ball and the other left uncrumpled, are released simultaneously from the same height above the floor. Which one, if either, do you expect to reach the floor first? Explain. a. The crumpled paper will reach the ground first because it will be less affected by air resistance. b. Both will reach the ground at the same time because their downward accelerations are identical. c. The flat paper will reach the ground first because it will glide to the floor more quickly.

a. The crumpled paper will reach the ground first because it will be less affected by air resistance. 3-3

A ball thrown straight upward moves initially with a decreasing upward velocity. What are the directions of the velocity and acceleration vectors during this part of the motion? a. The direction of the velocity vector is upward and the direction of the acceleration vector is downward. b. The directions of both the velocity vector and the acceleration vector are downward. c. The direction of the velocity vector is downward and the direction of the acceleration vector is upward. d. The directions of both the velocity vector and the acceleration vector are upward.

a. The direction of the velocity vector is upward and the direction of the acceleration vector is downward. 3-12a

Two identical cans, one filled with lead shot and the other with feathers, are dropped from the same height by a student standing on a chair. Which can, if either, experiences the greater force due to the gravitational attraction of the Earth? a. The lead shot-filled can experiences a greater force due to gravity because it contains more mass. b. Both cans experience the same force due to gravity because the force due to gravity is the same for all objects. c. The feather-filled can experiences a greater force due to gravity since the effect of air resistance is reduced by putting the feathers in the can.

a. The lead shot-filled can experiences a greater force due to gravity because it contains more mass. 4-13a

If a ball is whirled in a vertical circle with constant speed, at what point in the circle, if any, is the tension in the string the greatest? Explain. a. The tension is greatest at the lowest point in the circle when it is equal to the sum of the weight plus the mass times acceleration. b. The tension remains constant at all points along the circle, equal to the sum of the weight plus the mass times acceleration. c. The tension is greatest at the highest point in the circle when the the sum of the weight plus the mass times acceleration is a maximum.

a. The tension is greatest at the lowest point in the circle when it is equal to the sum of the weight plus the mass times acceleration. 5-10

A tortoise and a hare cover the same distance in a race. The hare goes very fast for brief intervals, but stops frequently, whereas the tortoise plods along steadily and finishes the race ahead of the hare. Which of the two racers has the greater average speed over the duration of the race? Explain. a. The tortoise has the greater average speed since he was the winner. b. The hare has the greater average speed since he can go faster. c. Their average speeds are equal. d. It's impossible to determine who had the greater average speed without collecting data.

a. The tortoise has the greater average speed since he was the winner. 2-1a

Is Kepler's third law valid for artificial satellites orbiting about the Earth? Explain. a. Yes, Kepler's third law applies to all satellite motion but in the case of satellites orbiting Earth the mass of the sun is replaced by the mass of the Earth so that there is a different ratio of T2/r3. b. No, Kepler's third law only applies to natural satellites orbiting the sun which demonstrate the ratio of T2/r3.

a. Yes, Kepler's third law applies to all satellite motion but in the case of satellites orbiting Earth the mass of the sun is replaced by the mass of the Earth so that there is a different ratio of T2/r3. 5-21

A ball is thrown downward with a large starting velocity. Will this ball reach the ground sooner than one that is just dropped at the same time from the same height? a. Yes, the thrown ball will reach the ground first. b. No, both balls will reach the ground at the same time. c. Whether the thrown ball reaches the ground first depends upon whether its acceleration when thrown is greater than the acceleration due to gravity.

a. Yes, the thrown ball will reach the ground first. 3-7a

Suppose that work is done on a large crate to tilt the crate so that it balances on one edge, as shown in the diagram, rather than sitting squarely on the floor as it was at first. Has the potential energy of the crate increased in this process? Explain. a. Yes, the weight of the crate has been lifted slightly so that if it is released, it will fall back and convert the potential energy into kinetic energy. b. No, although work was done on the crate, only the kinetic energy of the crate was increased as it was lifted. c. No, neither the potential or kinetic energy increased as the crate was tilted.

a. Yes, the weight of the crate has been lifted slightly so that if it is released, it will fall back and convert the potential energy into kinetic energy. 6-12

A ball on the end of a string is whirled with constant speed in a counterclockwise horizontal circle. At point A in the circle, the string breaks. Before the string breaks, is there a net force acting upon the ball? If so, what is its direction? Explain. a. Yes, there is a force radially inward due to the tension in the string that supplies the centripetal force needed for this motion. b. Yes, there is force solely due to the gravitational force of the Earth. c. No, the force radially inward due to the tension in the string balances the centripetal force resulting in a zero net force.

a. Yes, there is a force radially inward due to the tension in the string that supplies the centripetal force needed for this motion. 5-3

The gravitational force acting on a lead ball is much larger than that acting on a wooden ball of the same size. When both are dropped, does the lead ball accelerate at the same rate as the wooden ball? Explain. a. Yes, they both accelerate at the same rate but the forces are different because their masses are different. b. Yes, they will accelerate at the same rate but only if the effect of air resistance is negligible on the lead ball. c. No, they accelerate at the different rates because of their difference in size.

a. Yes, they both accelerate at the same rate but the forces are different because their masses are different. 4-7

A ball hangs from a string attached to the ceiling, what forces act on the ball? (Select all that apply.) a. tension from the string b. normal force c. force due to gravitation d. coulomb force Which of the following forces related to those identified in part (a) is a reaction force described by Newton's third law of motion? (Select all that apply.) a. normal force of ball on ceiling b. force of ball on string c. ball's gravitational force on earth d. coulomb force of ball on earth

a. and c. tension from the string and force due to gravity b. and c. force of the ball on string and ball's gravitational force on earth 4-15a,c

A boy sits at rest on the floor. What two vertical forces act upon the boy? (Select all that apply.) a. gravitational force b. frictional force c. coulomb force d. normal force Do these two forces constitute an action/reaction pair as defined by Newton's third law of motion? Explain. a. Yes, these forces constitute an action/reaction pair because they are equal in magnitude, opposite in direction, and acting on the same body. b. No, these forces do not constitute an action/reaction pair because although they are equal in magnitude and opposite in direction, they act on the same body. c. It is not possible to determine whether these forces constitute an action/reaction pair.

a. and d. gravitational force and normal force b. No, these forces do not constitute an action/reaction pair because although they are equal in magnitude and opposite in direction, they act on the same body. 4-14

A boy pushes his friend across a skating rink. Since the frictional forces are very small, the force exerted by the boy on his friend's back is the only significant force acting on the friend in the horizontal direction. Is the change in kinetic energy of the friend greater than, equal to, or less than the work done by the force exerted by the boy? Explain. a. The work done by the force exerted by the boy doing the pushing is greater than the change in kinetic energy since much of the work goes into moving his friend across the ice. b. In the absence of friction the work done by the force exerted by the boy doing the pushing is equal to the change in kinetic energy. c. The work done by the force exerted by the boy doing the pushing is less than the change in kinetic energy because the frictional forces on the ice are very small.

b. In the absence of friction the work done by the force exerted by the boy doing the pushing is equal to the change in kinetic energy. 6-7

A ball is thrown downward with a large starting velocity. Will this ball accelerate more rapidly than one that is dropped with no initial velocity? Explain. a. Yes, the acceleration of a falling object depends on initial velocity. b. No, both balls will accelerate the same due to gravity. c. Whether the thrown ball accelerates more rapidly depends on whether its initial velocity is proportional to its acceleration squared.

b. No, both balls will accelerate the same due to gravity. 3-7b

A ball thrown straight upward moves initially with a decreasing upward velocity. What are the directions of the velocity and acceleration vectors during this part of the motion? Does the acceleration also decrease? Explain. a. Yes, the acceleration decreases as the ball is thrown upward. b. No, the acceleration does not decrease but remains constant. c. No, the acceleration increases as the ball is thrown upward.

b. No, the acceleration does not decrease but remains constant. 3-12b

Two blocks with the same mass are connected by a string and are pulled across a frictionless surface by a constant force, F, exerted by a string (see diagram). O—O—F—> Will the two blocks move with constant velocity? Explain. a. Yes, the applied force is constant and implies a zero acceleration that results in a constant velocity. b. No, the applied force is constant and implies a constant acceleration that results in constantly increasing velocity. c. Whether the velocity is constant cannot be determined without knowing the magnitude of the force.

b. No, the applied force is constant and implies a constant acceleration that results in constantly increasing velocity. 4-17a

A ball is being twirled in a circle at the end of a string. The string provides the centripetal force needed to keep the ball moving in the circle at constant speed. Does the force exerted by the string on the ball do work on the ball in this situation? Explain. a. Yes, the tension in the string does work on ball to maintain its circular path. b. No, the tension in the string acts perpendicular to the instantaneous direction of the motion and, therefore, does no work. c. There is not enough information to determine whether the force exerted by the string does work on the ball.

b. No, the tension in the string acts perpendicular to the instantaneous direction of the motion and, therefore, does no work. 6-3

A man pushes very hard for several seconds on a heavy rock, but the rock does not budge. Has the man done any work on the rock? Explain. a. Yes, the man has done work on the rock because of the great force he exerted to move it. b. No, work has been done on the rock because the rock traversed no distance. c. There is not enough information to determine whether the man has done work on the rock or not.

b. No, work has been done on the rock because the rock traversed no distance. 6-2

The acceleration due to gravity on the moon is approximately one-sixth the gravitational acceleration near the Earth's surface. If a rock is transported from Earth to the moon, will either its mass or its weight change in the process? Explain. a. Only its mass will change since the standards used to measure mass are affected by the moon's weaker gravitational field. b. Only its weight will change because acceleration due to the moon's gravitational field is weaker than Earth's. c. Both the mass and weight will change since both properties are affected by the moon's gravitational field. d. Neither weight nor mass will change since the moon's gravitational field is so much weaker than that of Earth.

b. Only its weight will change because acceleration due to the moon's gravitational field is weaker than Earth's. 4-8

A car travels the same distance at constant speed around two curves, one with twice the radius of curvature of the other. For which of these curves is the change in velocity of the car greater? Explain. a. The change in velocity is greater for the curve with the larger radius since the car must travel farther for the same change in the angular direction. b. The change in velocity is greater for the curve with the smaller radius since the rate of change in the angular direction is greater. c. There is no difference in the change in velocity between the cars because they travel the same distance around their curves at the same speed.

b. The change in velocity is greater for the curve with the smaller radius since the rate of change in the angular direction is greater. 5-1

A tortoise and a hare cover the same distance in a race. The hare goes very fast for brief intervals, but stops frequently, whereas the tortoise plods along steadily and finishes the race ahead of the hare. Which of the two racers is likely to reach the greatest instantaneous speed during the race? Explain. a. The tortoise has the greater instantaneous speed since he was the winner. b. The hare has the greater instantaneous speed since he can go faster. c. Their instantaneous speeds are equal. d. It's impossible to determine who had the higher instantaneous speed without collecting data.

b. The hare has the greater instantaneous speed since he can go faster. 2-1b

In the diagram, two different trajectories are shown for a ball thrown by a center fielder to home plate in a baseball game. Which of the two trajectories (if either), the higher one or the lower one, will result in a longer time for the ball to reach home plate? Explain. a. The lower trajectory will result in a longer time because its initial vertical velocity component is smaller. b. The higher trajectory will result in a longer time because its initial vertical velocity component is larger. c. Both trajectories will result in the same amount of time because the horizontal distance traversed is the same.

b. The higher trajectory will result in a longer time because its initial vertical velocity component is larger. 3-22

Two blocks with the same mass are connected by a string and are pulled across a frictionless surface by a constant force, F, exerted by a string (see diagram). O—O—F—> Will the tension in the connecting string be greater than, less than, or equal to the force F? Explain. a. The tension in the connecting string will be greater than F. While both bodies have the same acceleration, the force F accelerates a total mass, 2m, and the force in the connecting string accelerates a mass, m, so it is twice F. b. The tension in the connecting string will be less than F. While both bodies have the same acceleration, the force F accelerates a total mass, 2m, and the force in the connecting string accelerates a mass, m, so it is half of F. c. The tension in the connecting string will be equal to F. Since both bodies have the same acceleration, the force F that accelerates the first mass and the force in the connecting string that accelerates the second mass must be equal.

b. The tension in the connecting string will be less than F. While both bodies have the same acceleration, the force F accelerates a total mass, 2m, and the force in the connecting string accelerates a mass, m, so it is half of F. 4-17b

A woman uses a pulley arrangement to lift a heavy crate. She applies a force that is one-fourth the weight of the crate, but moves the rope a distance four times the height that the crate is lifted. Is the work done by the woman greater than, equal to, or less than the work done by the rope on the crate? Explain. a. The work done by the woman is greater than the work done by the rope on the crate since she pulls the rope four times the distance traveled by the crate. b. The work done by the woman is equal to the work done by the rope on the crate because, although the force on the rope is one fourth the weight of the crate, the rope traveled four times the distance traveled by the crate. c. The work done by the woman is less than the work done by the rope on the crate because the force she applies on the rope is one fourth the weight of the crate while the force on the rope is equal to the weight of the crate.

b. The work done by the woman is equal to the work done by the rope on the crate because, although the force on the rope is one fourth the weight of the crate, the rope traveled four times the distance traveled by the crate. 6-4

Equal forces are used to move blocks A and B across the floor. Block A has twice the mass of block B, but block B moves twice the distance moved by block A. Which block, if either, has the greater amount of work done on it? Explain. a. The work done is twice as great for block A because it has twice the mass of block A. b. The work done is twice as great for block B because it is moved twice the distance of block A. c. The amount of work done on the blocks is equal.

b. The work done is twice as great for block B because it is moved twice the distance of block A. 6-1

A ball rolls off a table with a large horizontal velocity. Does the direction of the velocity vector change as the ball moves through the air? Explain. a. Yes, the velocity of the ball is in the x-direction while it rolls on the table and in the y-direction as it falls to the floor. b. Yes, although the horizontal component remains constant the vertical component increases downward, changing the resultant velocity vector. c. No, the velocity of the ball is constant in the x- and y-direction , so the direction of the velocity vector does not change.

b. Yes, although the horizontal component remains constant the vertical component increases downward, changing the resultant velocity vector. 3-18

If a curve is banked, is it possible for a car to negotiate the curve even when the frictional force is zero due to very slick ice? Explain. a. Yes, however, the car can only negotiate the curve at low speeds where slippage is negligible in the absence of a frictional force. b. Yes, on a banked curve the normal reaction force of the road on the car can provide a horizontal component yielding the correct centripetal force for a given speed. c. No, even around a banked curve the car cannot negotiate the curve without a horizontal component to yield the correct centripetal force for a given speed.

b. Yes, on a banked curve the normal reaction force of the road on the car can provide a horizontal component yielding the correct centripetal force for a given speed. 5-9

A car travels around a flat (nonbanked) curve with constant speed. Is there a maximum speed at which the car will be able to negotiate the curve? If so, what factors determine this maximum speed? Explain. a. Yes, the maximum speed depends upon the mass of the car and the experience of the driver. b. Yes, the maximum speed will depend upon the static friction of the surface and the radius of curvature of the road. c. No, there is no maximum speed as long as the car's speed around the curve is constant. d. No, there is no maximum speed for the car to round the curve provided the driver is experienced.

b. Yes, the maximum speed will depend upon the static friction of the surface and the radius of curvature of the road. 5-8

When a bow and arrow are cocked, a force is applied to the string to pull it back. Is the energy of the system increased? Explain. a. Yes, the work in cocking the bow and arrow has increased the kinetic energy of the bow-arrow system. b. Yes, the work in cocking the bow and arrow has gone into elastic potential energy to the bow. c. No, the energy of the bow-arrow system has remained constant.

b. Yes, the work in cocking the bow and arrow has gone into elastic potential energy to the bow. 6-14

A box is moved from the floor up to a tabletop but gains no speed in the process. Is there work done on the box, and if so, what has happened to the energy added to the system? a. Yes, work is done on the box to move it the height of the table; the work has gone into increasing the kinetic energy of the block-earth system. b. Yes, work is done on the box to move it the height of the table; the work has gone into increasing the potential energy of the block-earth system. c. No, there is no work done on the box because the box does not accelerate as it moves upward. d. No, there is no work done on the box because the displacement of the box is perpendicular to the force applied to it.

b. Yes, work is done on the box to move it the height of the table; the work has gone into increasing the potential energy of the block-earth system. 6-11

Does the speedometer on a car measure average speed or instantaneous speed? a. average speed b. instantaneous speed

b. instantaneous speed 2-2

Does a planet moving in an elliptical orbit about the sun move fastest when it is farthest from the sun or when it is nearest to the sun? Explain, by referring to one of Kepler's laws. a. A planet moves at the same speed at all positions along its elliptical orbit. b. A planet moves fastest when it is farthest from the sun because it traverses an equal area of the ellipse in the same time interval. c. A planet moves fastest when it is nearest to the sun because it traverses an equal area of the ellipse in the same time interval.

c. A planet moves fastest when it is nearest to the sun because it traverses an equal area of the ellipse in the same time interval. 5-13

Heliocentric models of the solar system (Copernican or Keplerian) require that the Earth rotate on its axis producing surface speeds of roughly 1000 MPH. If this is the case, why do we not feel this tremendous speed? Explain. a. Such heliocentric models are now considered inappropriate since such high surface speeds are unreasonable. b. High surface speeds are buffered by the atmosphere which rotates with equal magnitude but in a direction opposite to the rotation of the Earth. c. All objects around us are moving at the same speed, including the air, so there is no sense of motion relative to our surroundings. d. The rotation of the Earth on its axis results in surface winds and other weather effects.

c. All objects around us are moving at the same speed, including the air, so there is no sense of motion relative to our surroundings. 5-12

Aristotle stated that heavier objects fall faster than lighter objects. Was Aristotle wrong, or in any sense could Aristotle's view be considered correct? a. Aristotle was completely wrong since heavier objects and lighter objects always fall with the same acceleration due to gravity, as demonstrated in the moon landing. b. Aristotle was completely correct. Heavier objects always fall faster than lighter objects because the gravitational force is proportional to mass. c. Aristotle was wrong in the absence of air resistance. In the presence of air resistance, it is true that the shape and mass of a falling object can affect its acceleration.

c. Aristotle was wrong in the absence of air resistance. In the presence of air resistance, it is true that the shape and mass of a falling object can affect its acceleration. 3-5

A ball rolling rapidly along a tabletop rolls off the edge and falls to the floor. At the exact instant that the first ball rolls off the edge, a second ball is dropped from the same height. Which ball, if either, reaches the floor first? Explain. a. The rolling ball reaches the floor first because it has an initial velocity and the dropped ball does not. b. The dropped ball reaches the floor first because its velocity is only in the y-direction. c. Both balls reach the floor at the same time because they both have the same initial zero y-component of velocity.

c. Both balls reach the floor at the same time because they both have the same initial zero y-component of velocity. 3-17

Two identical cans, one filled with lead shot and the other with feathers, are dropped from the same height by a student standing on a chair. Which can, if either, experiences the greater acceleration due to gravity? Explain. a. The feather-filled can experiences a greater acceleration due to gravity since air resistance is reduced by putting the feathers in the can. b. The lead shot-filled can experiences a greater acceleration due to gravity because of its greater mass. c. Both cans experience the same acceleration due to gravity regardless of mass.

c. Both cans experience the same acceleration due to gravity regardless of mass. 4-13b

Two identical pieces of paper, one crumpled into a ball and the other left uncrumpled, are released simultaneously from inside the top of a large evacuated tube. Which one, if either, do you expect will reach the bottom of the tube first? a. The crumpled piece of paper b. The uncrumpled piece of paper c. Both the crumpled and the uncrumpted sheets of paper will reach the bottom of the tube at the same moment.

c. Both the crumpled and the uncrumpted sheets of paper will reach the bottom of the tube at the same moment. 3-4

Is the mass of an object the same thing as its weight? Explain. a. Yes, used interchangeably, mass and weight both indicate the amount of force resulting from an object under the influence of Earth's gravitational field. b. Yes, both mass and weight indicate the intrinsic property of matter demonstrated by an object's inertia. c. No, mass is an intrinsic property of matter, while weight is a force resulting from an object under the influence of Earth's gravitational field.

c. No, mass is an intrinsic property of matter, while weight is a force resulting from an object under the influence of Earth's gravitational field. 4-6

Is mass a force? Explain. a. Yes, mass is a force resulting from the acceleration due to a gravitational field. b. Yes, mass is equivalent to the inertial force that must be overcome to change the motion of an object. c. No, mass is not a force but a property of matter arising from the structure of matter.

c. No, mass is not a force but a property of matter arising from the structure of matter. 4-9

A ball is thrown straight upward. At the very top of its flight, the velocity of the ball is zero. Is its acceleration at this point also zero? Explain. a. Yes, the acceleration is zero because the velocity is also zero. b. Yes, the acceleration is zero because the ball is thrown straight upward. c. No, the acceleration due to gravity is constant even at the top of its flight. d. No, the acceleration is decreasing but will not be zero until the ball lands on the ground.

c. No, the acceleration due to gravity is constant even at the top of its flight. 3-13

A 3-kg block is observed to accelerate at a rate twice that of a 6-kg block. Is the net force acting on the 3-kg block twice as large as that acting on the 6-kg block? Explain. a. Yes, the force on the 3-kg block is twice as large since its acceleration is twice as large. b. No, the force on the 3-kg block is half as large since half the mass times the acceleration yields half the force. c. No, the forces on the blocks are equal since half the mass times twice the acceleration yields the same force. d. No, the force on the 3-kg block is one-fourth as large since half the mass times half the acceleration yields one-fourth the force.

c. No, the forces on the blocks are equal since half the mass times twice the acceleration yields the same force. 4-2

Does the sun exert a larger force on the Earth than that exerted on the sun by the Earth? Explain. a. Yes, the sun exerts a larger force because its mass is greater. b. No, the Earth exerts a larger force because its mass is smaller. c. No, the interaction of two masses results in equal but oppositely directed forces.

c. No, the interaction of two masses results in equal but oppositely directed forces. 5-14

Two balls of the same mass are accelerated by different net forces such that one ball gains a velocity twice that of the other ball in the process. Is the work done by the net force acting on the faster-moving ball twice that done on the slower-moving ball? Explain. a. Yes, the work done by the net force acting on the faster-moving ball is twice that of the slower-moving ball since the faster-moving ball is moving twice as fast. b. No, the work done on the faster ball is one-fourth the work done on the slower ball since the work goes into kinetic energy and kinetic energy is proportional to v2. c. No, the work done on the faster ball is four times the work done on the slower ball since the work goes into kinetic energy and kinetic energy is proportional to v2. d. No, the work done on the faster ball is half the work done on the slower ball since the faster-moving ball is moving twice as fast.

c. No, the work done on the faster ball is four times the work done on the slower ball since the work goes into kinetic energy and kinetic energy is proportional to v2. 6-8

In the diagram, two different trajectories are shown for a ball thrown by a center fielder to home plate in a baseball game. For either of the trajectories shown above, is the velocity of the ball equal to zero at the high point in the trajectory? Explain. a. Yes, the vertical velocity is zero at the high point of each of the trajectories so at that moment the velocity of the ball is equal to zero. b. Yes, the trajectory with the higher arch has a both a vertical and horizontal velocity of zero at the high point so the velocity of the ball is zero. c. No, there is always a horizontal velocity component not equal to zero so there is no time when the velocity of the ball is equal to zero for either of the shown trajectories.

c. No, there is always a horizontal velocity component not equal to zero so there is no time when the velocity of the ball is equal to zero for either of the shown trajectories. 3-23

Two equal-magnitude horizontal forces act on a box as shown in the diagram. Is it possible that the object is moving, given the fact that the two forces acting on it are equal in size but opposite in direction? Explain. a. Yes, it is moving, given the fact that the two forces acting on it are equal in size but opposite in direction. b. No, it is not moving, given the fact that the two forces acting on it are equal in size but opposite in direction. c. The object may or may not be moving, but it won't be accelerating.

c. The object may or may not be moving, but it won't be accelerating. 4-3

Did Ptolemy's view of the solar system require motion of the Earth, rotational or otherwise? Explain. a. The stars were stationary while the Earth and planets revolved around them in their epicycles. b. The center of the universe was stationary while the Earth and planets revolved around it in their epicycles. c. The sun was stationary while the stars, Earth, and other planets revolved around it in their epicycles. d. The Earth was stationary and the sun and the planets and stars revolved about it in their epicycles.

d. The Earth was stationary and the sun and the planets and stars revolved about it in their epicycles. 5-11

Two equal forces act on two different objects, one of which has a mass ten times as large as the other. Will the more massive object have a larger acceleration, an equal acceleration, or a smaller acceleration than the less massive object? Explain. a. The acceleration of the larger mass is equal to the acceleration of the smaller mass since the ratio of the accelerations will be equal to the ratio of the masses. b. There is not enough information to determine the relative accelerations. c. The larger mass has a larger acceleration since the ratio of the accelerations will be proportional to the ratio of the masses. d. The larger mass has a smaller acceleration since the ratio of the accelerations will be the inverse of the ratio of the masses.

d. The larger mass has a smaller acceleration since the ratio of the accelerations will be the inverse of the ratio of the masses. 4-1

A ball hangs from a string attached to the ceiling, what is the net force acting on the ball? Explain. a. The net force on the ball is the force due to the tension in the string. b. The net force is the sum of the magnitudes of the tension in the string and the force due to gravitation. c. The net force on the ball is the force due to gravitation d. The net force equals zero because the ball is not accelerating in any direction.

d. The net force equals zero because the ball is not accelerating in any direction. 4-15b

Three equal masses are located as shown in the diagram. What is the direction of the net force acting on m2? Explain. m1 m2 m3 ----O----O----------O----- a. There is not enough information to determine the direction of the net force acting on m2. b. The net force will act to the right because the force exerted by m3 on m2 will be greater than the force exerted by m1 on m2 because m1 is closer than m3. c. The net force is zero because the force exerted by m3 on m2 will be equal to the force exerted by m1 on m2 because the masses are equal. d. The net force will act to the left because the force exerted by m1 on m2 will be greater than the force exerted by m3 on m2 because m1 is closer than m3.

d. The net force will act to the left because the force exerted by m1 on m2 will be greater than the force exerted by m3 on m2 because m1 is closer than m3. 5-15