Physics207

6.3.1. An elevator supported by a single cable descends a shaft at a constant speed. The only forces acting on the elevator are the tension in the cable and the gravitational force. Which one of the following statements is true? a) The work done by the tension force is zero joules. b) The net work done by the two forces is zero joules. c) The work done by the gravitational force is zero joules. d) The magnitude of the work done by the gravitational force is larger than that done by the tension force. e) The magnitude of the work done by the tension force is larger than that done by the gravitational force.

B

6.5.1. Two balls of equal size are dropped from the same height from the roof of a building. One ball has twice the mass of the other. When the balls reach the ground, how do the kinetic energies of the two balls compare? a) The lighter one has one fourth as much kinetic energy as the other does. b) The lighter one has one half as much kinetic energy as the other does. c) The lighter one has the same kinetic energy as the other does. d) The lighter one has twice as much kinetic energy as the other does. e) The lighter one has four times as much kinetic energy as the other does.

B

Problem 6.51, modified. A projectile of mass 2 kg is shot straight up with an initial kinetic energy of Ki and reaches a maximum height of 12 m. The average force due to air resistance on the projectile during its ascent has a magnitude of 6 N. Complete the following statement: As the projectile moves from the launch point to maximum height, the mechanical energy of the projectile-Earth system a. Remains the same. b. Decreases. c. Increases

B

Some children are practicing catching baseballs. The coach tosses the ball into the air and hits the ball with his bat. The ball travels nearly horizontally, directly at the short stop who manages to catch the line drive. Did the coach, via the bat, do any work on the ball as it was hit? a) No, it travels nearly horizontally, and no work is done. b) Yes, work was done on the ball because during the time the force acted on the ball, the bat and ball moved through some distance. c) No, there was a force acting on the ball, but there was no displacement while the force was acting. d) Yes, work was done on the ball because the force of gravity was acting on the ball while it was being hit. e) No work was done on the ball because the ball flew even though the force was no longer acting on it.

B

The initial velocity of a 4-kg box is 10 m/s, due west. After the box slides 3.0 m horizontally, its speed is 2 m/s. Determine the magnitude of the non-conservative force acting on the box as it slides, assuming the force points against the motion. a. 8N b. 64N c. 192N d. 200N e. 576N

B

Which force is responsible for holding a car in an unbanked curve? a. the reaction force to the car's weight b. the force of friction c. the car's weight d. the vertical component of the normal force e. the horizontal component of the normal force

B

You are pulling an object along a rough surface. The magnitude of the displacement is 10 m. The work done by the frictional force is a. Positive b. Negative c. Zero d. Not enough information to answer this question

B

5.4.4. A 1000-kg car travels along a straight portion of highway at a constant velocity of 10 m/s, due east. The car then encounters an unbanked curve of radius 50 m. The car follows the curve traveling at a constant speed of 10 m/s while the direction of the car changes from east to south. What is the magnitude of the frictional force between the tires and the road as the car negotiates the unbanked curve? a) 500 N b) 1000 N c) 2000 N d) 5000 N e) 10000N

C

7.1.9. Three events are observed at a baseball game: I. A baseball is thrown by a pitcher. It starts from rest and is traveling at +38 m/s as it flies toward the catcher. II. A baseball is traveling at +38 m/s when it enters the catcher's glove and stops. III. A baseball is traveling at +38 m/s when it hits a wall and bounces away from the wall at 38 m/s. The change in the momentum of the baseball has the largest magnitude in which case(s)? a) I only b) II only c) III only d) IandIIonly e) II and III only

C

A 0.50-kg bomb is sliding along an icy pond (frictionless surface) with a velocity of 2.0 m/s to the west. The bomb explodes into two pieces. After the explosion, a 0.20-kg piece moves south at 4.0 m/s. What are the components of the velocity of the 0.30-kg piece? a. 4.0 m/s north, 2.7 m/s west b. 0 m/s, 2.0 m/s east c. 2.7 m/s north, 3.3 m/s west d. 4.0 m/s north, 2.0 m/s east e. 4.0 m/s north, 0 m/s

C

A 10 kg toy roller coaster starts from rest at the top of an 18-m hill as shown. The car travels to the bottom of the hill and continues up the next hill that is 10.0 m high. What is the kinetic energy at the top of the 10.0-m hill, if friction is ignored? a) 1800 J b) 1000 J c) 800J d) 40 J e) 100J

C

A 1000-kg car travels along a straight portion of highway at a constant velocity of 10 m/s, due east. The car then encounters an unbanked curve of radius 50 m. The car follows the curve traveling at a constant speed of 10 m/s while the direction of the car changes from east to south. What is the magnitude of the frictional force between the tires and the road as the car negotiates the unbanked curve? a) 500N b) 1000 N c) 2000 N d) 5000 N e) 10 000 N

C

A 1800-kg Jeep travels along a straight 500-m portion of highway (from A to B) at a constant speed of 10 m/s. At B, the Jeep encounters an unbanked curve of radius 50 m. The Jeep follows the road from B to C traveling at a constant speed of 10 m/s while the direction of the Jeep changes from east to south. What is the magnitude of the acceleration of the Jeep as it travels from B to C? a. zero m/s2 b. 20 m/s2 c. 2 m/s2 d. 10 m/s2 e. 5 m/s2

C

A donkey pulls a crate up a rough, inclined plane at constant speed. Which one of the following statements concerning this situation is false? a. The donkey does "positive" work in pulling the crate up the incline. b. The gravitational potential energy of the crate is increasing. c. The work done on the object by gravity is zero joules. d. The work done on the crate by the normal force of the plane is zero joules. e. The net work done by all the forces acting on the crate is zero joules.

C

7.2.1. A 9-kg object is at rest. Suddenly, it explodes and breaks into two pieces. The mass of one piece is 6 kg and the other is a 3-kg piece. Which one of the following statements concerning these two pieces is correct? a) The speed of the 6-kg piece will be one eighth that of the 3-kg piece. b) The speed of the 3-kg piece will be one fourth that of the 6-kg piece. c) The speed of the 6-kg piece will be one fourth that of the 3-kg piece. d) The speed of the 3-kg piece will be one half that of the 6-kg piece. e) The speed of the 6-kg piece will be one half that of the 3-kg piece.

E

7.1.2. A football of mass m, initially at rest, is kicked so that leaves the foot at a speed v. If t represents the duration of the collision between the ball and the foot, which one of the following expressions determines the magnitude of the average force exerted on the ball? a) mvt b) (1/2)mv2 c) (1/2)mv2/t d) mv/t e) (1/2)mvt2

D

A ball is whirled on the end of a string in a horizontal circle of radius R at constant speed v. By which one of the following means can the centripetal acceleration of the ball be increased by a factor of two? a) Keep the radius fixed and increase the period by a factor of two. b) Keep the radius fixed and decrease the period by a factor of two. c) Keep the speed fixed and increase the radius by a factor of two. d) Keep the speed fixed and decrease the radius by a factor of two. e) Keep the radius fixed and increase the speed by a factor of two.

D

A car is up on a hydraulic lift at a garage. The wheels are free to rotate, and the drive wheels are rotating with a constant angular velocity. Which one of the following statements is true? a. A point on the rim has no tangential acceleration and no centripetal acceleration. b. A point on the rim has both a nonzero tangential acceleration and a nonzero centripetal acceleration. c. A point on the rim has a nonzero tangential acceleration but no centripetal acceleration. d. A point on the rim has no tangential acceleration but does have a nonzero centripetal acceleration.

D

A force in the negative direction of an x axis is applied for 20 ms to a ball, which initially has a momentum +12 𝑘𝑔 ∙ 𝑚/𝑠 𝑥. The force varies in magnitude, and the impulse has a magnitude 20 Ns. What is the ball's momentum just after the force is applied? a. 32𝑘𝑔∙𝑚/𝑠𝑥 b. −32𝑘𝑔∙𝑚/𝑠 𝑥 c. 4.8𝑘𝑔∙𝑚/𝑠 𝑥 d. −8𝑘𝑔∙𝑚/𝑠𝑥 e. 240𝑘𝑔∙𝑚/𝑠 𝑥

D

A 1500-kg elevator moves upward with constant speed through a vertical distance of 30 m. How much work was done by the tension in the elevator cable? a. 380 000 J b. 990 J c. 140 000 J d. 8100 J e. 450 000 J

E

A high school baseball pitcher can typically throw a ball at 22 m/s. Professional baseball pitchers can throw the ball with twice that speed, but few others can. To see why this is the case, determine the difference in the kinetic energy of a baseball thrown at v m/s and one thrown at 2v m/s and express the difference as a percentage. a) 50% b) 100% c) 200% d) 300% e) 400%

D

A long, thin rod of length 4L rotates counterclockwise with constant angular acceleration around an axis that is perpendicular to the rod and passes through a pivot point that is a length L from one end as shown. What is the ratio of the tangential acceleration at a point on the end closest to the pivot point to that at a point on the end farthest from the pivot point? a) 4 b) 3 c) 1/2 d) 1/3 e) 1/4

D

A model airplane has a mass of 0.90 kg and moves at a constant speed on a circle that is parallel to the ground. The path of the airplane and its guideline lie in the same horizontal plane, because the weight of the plane is balanced by the lift generated by its wings. Which of the following statements is false? a) The work done by the lift force is zero b) The work done by the plane's weight is zero c) The work done by the tension force is zero d) The net work done on the plane is not zero

D

A very massive object traveling at 10 m/s strikes a light object, initially at rest, and the light object moves off in the direction of travel of the heavy object. If the collision is elastic, the speed of the lighter object is a. 5m/s b. 10 m/s c. 15 m/s d. 20 m/s e. Not enough information

D

Mike is cutting the grass using a human-powered lawn mower. He pushes the mower with a force of 52 N directed at an angle of 41° below the horizontal direction. Calculate the work that Mike does on the mower each time he pushes it 9.1 m across the yard. a. 310 J b. 510 J c. 260 J d. 360 J e. 410J

D

The drawing shows identical empty fuel tanks about to be released by three different jet planes. At the moment of release, each plane has the same speed, and each tank is at the same height above the ground. However, the directions of the velocities of the planes are different. Which tank has the largest speed upon hitting the ground? a. A b. B c. C d. All tie

D

The drawing shows two 4.5-kg balls located on the y axis at 1.0 and 9.0 m, respectively, and a third ball with a mass 2.3 kg which is located at 6.0 m. What is the location of the center of mass of this system? a. 4.8 m b. 5.6m c. 6.0 m d. 5.2m e. 6.4m

D

The drawing shows two 4.5-kg balls located on the y axis at 1.0 and 9.0 m, respectively, and a third ball with a mass 2.3 kg which is located at 6.0 m. What is the location of the center of mass of this system? a. 4.8 m b. 5.6 m c. 6.0 m d. 5.2 m e. 6.4 m

D

The kinetic energy of a car is 8x106 J as it travels along a horizontal road. How much power is required to stop the car in 10 s? a. 8x106 W b. 8x107 W c. 8x104 W d. 8x105 W e. Zero watts

D

Which one of the following statements concerning a wheel undergoing rolling motion is true? a) The linear velocity for all points on the rim of the wheel is non-zero. b) The tangential velocity is the same for all points on the wheel. c) The tangential velocity is the same for all points on the rim of the wheel. d) There is no slipping at the point where the wheel touches the surface on which it is rolling. e) The angular acceleration of the wheel must be zero m/s2.

D

5.3.3. A ball is attached to a string and whirled in a horizontal circle. The ball is moving in uniform circular motion when the string separates from the ball (the knot wasn't very tight). Which one of the following statements best describes the subsequent motion of the ball? a) The ball immediately flies in the direction radially outward from the center of the circular path the ball had been following. b) The ball continues to follow the circular path for a short time, but then it gradually falls away. c) The ball gradually curves away from the circular path it had been following. d) The ball immediately follows a linear path away from, but not tangent to the circular path it had been following. e) The ball immediately follows a line that is tangent to the circular path the ball had been following

E

A 2.0-kg solid disk rolls without slipping on a horizontal surface so that its center proceeds to the right with speed 5.0 m/s. The point A is the uppermost point on the disk and the point B is along the horizontal line that connects the center of the disk to the rim. What is the instantaneous speed of point A with respect to the ground? a. 5.0 m/s b. 7.1 m/s c. zero m/s d. 2.5 m/s e. 10.0 m/s

E

A 2.0-kg solid disk rolls without slipping on a horizontal surface so that its center proceeds to the right with speed 5.0 m/s. The point A is the uppermost point on the disk and the point B is along the horizontal line that connects the center of the disk to the rim. What is the instantaneous speed of the point of the disk that makes contact with the surface? a. 5.0 m/s b. 7.1 m/s c. 7.5 m/s d. 10.0 m/s e. zero m/s

E

A ball is whirled on the end of a string in a horizontal circle of radius R at constant speed v. Complete the following statement: The centripetal acceleration of the ball can be increased by a factor of 4 by: a. Keeping the speed fixed and increasing the radius by a factor of 4. b. Keeping the radius fixed and increasing the speed by a factor of 4. c. Keeping the radius fixed and increasing the period by a factor of 4. d. Keeping the radius fixed and decreasing the period by a factor of 4. e. Keeping the speed fixed and decreasing the radius by a factor of 4.

E

A car is traveling at 10 m/s. The driver applies the brakes and friction brings the car to a stop after it slides a distance d. If the car's speed was 20 m/s, what would the stopping distance be? a. d/4 b. d/2 c. d d. 2d e. 4d

E

A certain string just breaks when it is under 15 N of tension. A boy uses this string to whirl a 0.75-kg stone in a horizontal circle of radius 2.0 m. The boy continuously increases the speed of the stone. At approximately what speed will the string break? a. 8.2 m/s b. 18 m/s c. 12 m/s d. 15 m/s e. 6.3 m/s

E

A net external nonconservative force does positive work on a particle. Based solely on this information, you are justified in reaching only one of the following conclusions. Which one is it? a) The kinetic and potential energies of the particle both decrease. b) The kinetic and potential energies of the particle both increase. c) Neither the kinetic nor the potential energy of the particle changes. d) The total mechanical energy of the particle decreases. e) The total mechanical energy of the particle increases.

E

A rancher puts a hay bail into the back of her SUV. Later, she drives around an unbanked curve with a radius of 48 m at a speed of 16 m/s. What is the minimum coefficient of static friction for the hay bail on the floor of the SUV so that the hay bail does not slide while on the curve? a) This cannot be determined without knowing the mass of the hay bail. b) 0.17 c) 0.33 d) 0.42 e) 0.54

E

A rock is thrown straight up from the surface of the Earth. Which one of the following statements describes the energy transformation of the rock as it rises? Neglect air resistance. a. Both the kinetic energy and the potential energy of the rock remain the same. b. The kinetic energy increases and the potential energy decreases. c. The total energy of the rock increases. d. Both the potential energy and the total energy of the rock increase. e. The kinetic energy decreases and the potential energy increases.

E

A roller coaster starts from rest at the top of an 18-m hill as shown. The car travels to the bottom of the hill and continues up the next hill that is 10.0 m high. How fast is the car moving at the top of the 10.0-m hill, if friction is ignored? a. 6.4 m/s b. 8.1 m/s c. 18 m/s d. 27 m/s e. 13 m/s

E

A sled of mass m is coasting on the icy surface of a frozen river. While it is passing under a bridge, a package of equal mass m is dropped straight down and lands on the sled (without causing any damage). The sled plus the added load then continue along the original line of motion. How does the kinetic energy of the (sled + load) compare with the original kinetic energy of the sled? a. It is twice the original kinetic energy of the sled. b. It is the same as the original kinetic energy of the sled. c. It is 3/4 the original kinetic energy of the sled. d. It is 1/4 the original kinetic energy of the sled. e. It is 1/2 the original kinetic energy of the sled.

E

A stone is thrown with a speed v0 and returns to earth, as the drawing shows. Ignore friction and air resistance, and consider the initial and final locations of the stone. Which one of the following correctly describes the change ΔU in the gravitational potential energy and the change ΔK in the kinetic energy of the stone at the two locations? Assume that the initial and final position are at the same level. a. U is negative and K is positive b. U is negative and K is negative c. U = 0 and K is negative d. U is positive and K is negative e. U = 0 and K = 0

E

Over a certain time interval, an object's velocity changes from 3.0 m/s due east to 3.0 m/s due west. If the mass of the object is 2.0 kg, how much work is done by the net force over this time interval? a. 9 J b. 18 J c. -9J d. -18 J e. 0 J

E

Which force is responsible for holding a car in a frictionless banked curve? a) the reaction force to the car's weight b) the vertical component of the car's weight c) the vertical component of the normal force d) the horizontal component of the car's weight e) the horizontal component of the normal force

E

Which one of the following statements concerning center of mass is true? a) The center of mass of an object must be located within the object. b) The center of mass of a system of objects cannot change even if there are forces acting on the objects. c) The velocity of the center of mass of a system of objects is greatly affected by a collision of objects within the system. d) All of an object's mass is located at its center of mass. e) The velocity of the center of mass of a system of objects is constant when the sum of the external forces acting on the system is zero.

E

Which one of the following statements concerning center of mass is true? a. The center of mass of an object must be located within the object. b. The center of mass of a system of objects cannot change even if there are forces acting on the objects. c. The velocity of the center of mass of a system of objects is greatly affected by a collision of objects within the system. d. All of an object's mass is located at its center of mass. e. The velocity of the center of mass of a system of objects is constant when the sum of the external forces acting on the system is zero.

E

5.3.1. A boy is whirling a stone at the end of a string around his head. The string makes one complete revolution every second, and the tension in the string is FT. The boy increases the speed of the stone, keeping the radius of the circle unchanged, so that the string makes two complete revolutions per second. What happens to the tension in the sting? a) The tension increases to four times its original value. b) The tension increases to twice its original value. c) The tension is unchanged. d) The tension is reduced to one half of its original value. e) The tension is reduced to one fourth of its original value.

A

In Fig. 8-33, a small block of mass m can slide along the frictionless loop-the-loop, with loop radius R. The block is released a point P, at height h = 5R. How much work is done by gravity when the block slides from Q to top of the loop (point T)? a. mgR b. 3mgR c. 4mgR d. 5mgR e. None of the above

A

Mass m1 = 10 kg and has a velocity of +15 m/s. It collides elastically with a stationary mass m2 = 10 kg. If the collision is head-on, what is the velocity of m1 after the collision? a. -15m/s b. -10 m/s c. -5 m/s d. 0m/s e. 15m/s

A

Mass m1 = 10 kg and has a velocity of +15 m/s. It collides elastically with a stationary mass m2 = 10 kg. If the collision is head-on, what is the velocity of m2 after the collision? a. -15m/s b. -10 m/s c. -5 m/s d. 0m/s e. 15m/s

A

Mass m1 has an initial velocity v0. If m1 experiences a perfectly inelastic collision with a stationary mass m2, the common velocity vf of the two masses after they became coupled is a. Less than v0. b. Equal to v0. c. Greater than v0. d. Either a or b e. Either b or c.

A

Two points are located on a rigid wheel that is rotating with decreasing angular velocity about a fixed axis. Point A is located on the rim of the wheel and point B is halfway between the rim and the axis. Which one of the following statements concerning this situation is true? a) Both points have the same instantaneous angular velocity. b) Each second, point A turns through a greater angle than point B. c) Both points have the same centripetal acceleration. d) Both points have the same tangential acceleration. e) The angular velocity at point A is greater than that of point B.

A

Two points are located on a rigid wheel that is rotating with decreasing angular velocity about a fixed axis. Point A is located on the rim of the wheel and point B is halfway between the rim and the axis. Which one of the following statements concerning this situation is true? a. Both points have the same instantaneous angular velocity. b. Each second, point A turns through a greater angle than point B. c. Both points have the same centripetal acceleration. d. Both points have the same tangential acceleration. e. The angular velocity at point A is greater than that of point B.

A

Which one of the following choices represents the largest kinetic energy? a) Mars is moving in its orbit around the Sun. b) A cyclist is racing in the annual Tour de France bicycle race. c) A leaf falls from a tree. d) A cheetah runs at its maximum speed to catch a fleeing zebra. e) An oil tanker sails through the Panama Canal.

A

A multiple-stage rocket is moving in outer space with a momentum of +150 000 kg · m/s. There are no external forces acting on the rocket. The rocket then separates into two stages, each of which moves along the same direction (either forward or backward) as the initial rocket. The table lists five possibilities for the momenta of the two stages. There is only one possibility that can be correct. Which is it?

+ 250,000 -100,000

6.5.7. Two identical balls are thrown from the same height from the roof of a building. One ball is thrown upward with an initial speed v. The second ball is thrown downward with the same initial speed v. When the balls reach the ground, how do the kinetic energies of the two balls compare? Ignore any air resistance effects. a) The kinetic energies of the two balls will be the same. b) The first ball will have twice the kinetic energy as the second ball. c) The first ball will have one half the kinetic energy as the second ball. d) The first ball will have four times the kinetic energy as the second ball. e) The first ball will have three times the kinetic energy as the second ball.

A

A 0.01-kg bullet moving at 900 m/s strikes a 0.8-kg wooden block at rest on a frictionless surface. The bullet emerges from the block, traveling in the same direction with its speed reduced to 500 m/s. What is the momentum of the block after the bullet emerges from the block? a. 4 kg·m/s b. 5 kg·m/s c. 9 kg·m/s d. 400 kg·m/s e. 720 kg·m/s

A

A 40-kg girl is bouncing on a trampoline. During a certain interval after she leaves the surface of the trampoline, her kinetic energy decreases to 210 J from 450 J. How high does she rise during this interval? Ignore air resistance. a. 0.6m b. 0.53 m c. 1.65 m d. 1.1m e. 0.83 m

A

A boy is whirling a stone around his head by means of a string. The string makes one complete revolution every second; and the magnitude of the tension in the string is F. The boy then slows down the stone, keeping the radius of the circle unchanged, so that the string makes one-half of a complete revolution every second. What happens to the tension in the sting? a. The magnitude of the tension reduces to one-fourth of its original value, F/4. b. The magnitude of the tension is unchanged. c. The magnitude of the tension increases to twice its original value, 2F. d. The magnitude of the tension reduces to half of its original value, F/2. e. The magnitude of the tension increases to four times its original value, 4F.

A

A man (mass m1 = 70 kg) and a woman (mass m2 = 60 kg) are standing at rest on a frictionless surface and holding opposite ends of the same rope. Then, the man pulls on the rope so that there is a tension in the rope. If the tension in the rope is 100 N, what is the acceleration of the center of mass of the man-woman system? a. 0 m/s2 b. 0.77 m/s2 c. 1.4 m/s2 d. 1.5 m/s2 e. 1.7 m/s2

A

A skier is sliding down a mountain. If friction is NOT negligible, which of the following statements must be true? a. Kinetic energy is increasing. b. Potential energy is increasing. c. Mechanical energy is conserved. d. Mechanical energy is decreasing. e. The skier is accelerating.

A

A skier is sliding down a mountain. Which of the following statements is correct if friction is negligible? a. U is transferred to K. b. K is transferred to U. c. The mechanical energy is increasing. d. Kinetic energy is constant. e. Both (b) and (c).

A

A sled of mass m is coasting on the icy surface of a frozen river. While it is passing under a bridge, a package of equal mass m is dropped straight down and lands on the sled (without causing any damage). The sled plus the added load then continue along the original line of motion. How does the speed of the (sled + load) compare with the original speed of the sled? a. It is twice the original speed of the sled. b. It is the same as the original speed of the sled. c. It is 3/4 the original speed of the sled. d. It is 1/4 the original speed of the sled. e. It is 1/2 the original speed of the sled.

A

A stationary 5-kg shell explodes into three pieces. Two of the fragments have a mass of 2 kg each and move along the paths shown with a speed of 10 m/s. The third fragment moves upward as shown. What is the speed of the third fragment? a. 20 m/s b. 1 m/s c. zero m/s d. 10 m/s e. 5 m/s

A

Car One is traveling due north and car Two is traveling due east. After the collision shown, Car One rebounds in the due south direction. Which of the numbered arrows is the only one that can represent the final direction of Car Two? a. 1 b. 2 c. 3 d. 4 e. 5

A

Complete the following statement: A collision is elastic if a. The total kinetic energy is conserved. b. The final kinetic energy is zero. c. The final momentum is zero. d. The objects stick together. e. Cats are involved.

A

Complete the following statement: Momentum will be conserved in a two-body collision only if a. The net external force acting on the two-body system is zero. b. The internal forces of the two body system cancel in action- reaction pairs. c. Both bodies come to rest. d. The kinetic energy of the system is conserved. e. The collision is perfectly elastic.

A

Complete the following statement: The maximum speed at which a car can safely negotiate an unbanked curve depends on all of the following factors except a) the coefficient of kinetic friction between the road and the tires. b) the coefficient of static friction between the road and the tires. c) the acceleration due to gravity. d) the diameter of the curve. e) the ratio of the static frictional force between the road and the tires and the normal force exerted on the car.

A

Figure 9-30 shows a snapshot of block 1 as it slides along an x axis on a frictionless floor, before it undergoes an elastic collision with stationary block 2. The figure also shows three possible positions of the center of mass (com) of the two- block system at the time of the snapshot. (Point B is halfway between the centers of the two blocks). Which statement describes the motion of block 1 after the collision if the com is located at point B? a. Block 1 is stationary b. Block 1 is moving forward c. Block 1 is moving backward d. Block 1 is either moving forward or backward.

A

Force F1 acts on a particle and does work W1. Force F2 acts simultaneously on the particle and does work W2. The speed of the particles does not change. What must be true. a. w1 = -w2 b. w1 is positive and w2 is positive c. w1 is zero and w2 is positive d. w1 is positive and w2 is zero

A

Imagine you are swinging a bucket by the handle around in a circle that is nearly level with the ground (a horizontal circle). Now imagine there's a ball in the bucket. What force keeps the ball moving in a circular path? a) contact force of the bucket on the ball b) contact force of the ball on the bucket c) gravitational force on the ball d) the centripetal force e) the centrifugal force

A

7.1.3. During the filming of a movie, a stunt person jumps from the roof of a tall building, but no injury occurs because the person lands on a large, air-filled bag. Which one of the following best describes why no injury occurs? a) The bag increases the amount of time the force acts on the person and reduces the change in momentum. b) The bag increases the amount of time during which the momentum is changing and reduces the average force on the person. c) The bag decreases the amount of time during which the momentum is changing and reduces the average force on the person. d) The bag provides the necessary force to stop the person. e) The bag reduces the impulse to the person.

B

A 0.065-kg tennis ball moving to the right with a speed of 15 m/s is struck by a tennis racket, causing it to move to the left with a speed of 15 m/s. If the ball remains in contact with the racquet for 0.020 s, what is the magnitude of the average force exerted on the ball? a. zero newtons b. 98N c. 160 N d. 240 N e. 320 N

B

A 0.2-kg steel ball is dropped straight down onto a hard, horizontal floor and bounces straight up. The ball's speed just before and just after impact with the floor is 10 m/s. Determine the magnitude of the impulse delivered to the floor by the steel ball. a. 2N·s b. 4N·s c. 20 N·s d. 200 N·s e. 0N·s

B

A 1000-kg car travels along a straight portion of highway at a constant velocity of 10 m/s, due east. The car then encounters an unbanked curve of radius 50 m. The car follows the curve traveling at a constant speed of 10 m/s while the direction of the car changes from east to south. What is the magnitude of the acceleration of the car as it travels the unbanked curve? a) zero m/s2 b) 2 m/s2 c) 5 m/s2 d) 10 m/s2 e) 20 m/s2

B

A high school physics teacher also happens to be the junior hockey team coach. During a break at practice, the coach asks two players to go to the center of the ice with a 10.0-m pole. A 40-kg player is at one end of the pole and a 60-kg player is at the other end. The players then start pulling themselves together by pulling the rod and sliding on the ice as they move along the rod. When the two players meet, what distance will the 60-kg player have moved? a) zero m b) 4.0m c) 5.0 m d) 6.0m e) 10.0 m

B

A merry-go-round at a playground is a circular platform that is mounted parallel to the ground and can rotate about an axis that is perpendicular to the platform at its center. The angular speed of the merry-go-round is constant, and a child at a distance of 1.4 m from the axis has a tangential speed of 2.2 m/s. What is the tangential speed of another child, who is located at a distance of 2.1 m from the axis? a. 1.5 m/s b. 3.3 m/s c. 2.2 m/s d. 5.0 m/s e. 0.98 m/s

B

Air resistance is a nonconservative force. It always opposes the motion of an object. An airplane flies from New York to Atlanta and then returns to its point of departure. The net work done by air resistance during this round trip is: a. zero b. negative c. negative for higher speeds and positive for slower speeds. d. negative for slower speeds and positive for higher speeds. e. positive

B

Complete the following statement: A collision is elastic if a. the final velocities are zero. b. the total kinetic energy is conserved. c. the objects stick together. d. the final kinetic energy is zero. e. the final momentum is zero.

B

Consider the following situations: (i) A minivan is following a hairpin turn on a mountain road at a constant speed of twenty miles per hour. (ii) A parachutist is descending at a constant speed 10 m/s. (iii) A heavy crate has been given a quick shove and is now sliding across the floor. (iv) Jenny is swinging back and forth on a swing at the park. (v) A football that was kicked is flying through the goal posts. (vi) A plucked guitar string vibrates at a constant frequency. In which one of these situations does the object or person experience zero acceleration? a) i only b) ii only c) iii and iv only d) iv, v, and vi only e) all of the situations

B

Figure 9-30 shows a snapshot of block 1 as it slides along an x axis on a frictionless floor, before it undergoes an elastic collision with stationary block 2. The figure also shows three possible positions of the center of mass (com) of the two- block system at the time of the snapshot. (Point B is halfway between the centers of the two blocks). Which statement describes the motion of block 1 after the collision if the com is located at point A? a. Block 1 is stationary b. Block 1 is moving forward c. Block 1 is moving backward d. Block 1 is either moving forward or backward.

B

In Fig. 8-33, a small block of mass m can slide along the frictionless loop-the-loop, with loop radius R. The block is released a point P, at height h = 5R. How much work is done by gravity when the block slides from P to top of the loop (point T)? a. mgR b. 3mgR c. 4mgR d. 5mgR e. None of the above

B

In which of the following circumstances is mechanical energy conserved, even though a nonconservative force acts on the moving object? a) The nonconservative force points in the same direction as the displacement of the object. b) The nonconservative force is perpendicular to the displacement of the object. c) The nonconservative force has a component that points in the same direction as the displacement of the object. d) The nonconservative force has a direction that is opposite to the displacement of the object. e) The nonconservative force has a component that points opposite to the displacement of the object.

B

Kevin is refinishing his rusty wheelbarrow. He moves his sandpaper back and forth 45 times over a rusty area, each time moving a total distance of 0.15 m. Kevin pushes the sandpaper against the surface with a normal force of 1.8 N. The coefficient of friction for the metal/sandpaper interface is 0.92. How much work is done by the kinetic frictional force during the sanding process? a) +11J b) -11 J c) +22J d) -22 J e) zero J

B

Mass m1 has an initial velocity v0. Mass m1 collides with a stationary mass m2. The net external force on the two particle system is zero. If the two masses stick together after the collision, then a. Both momentum and kinetic energy is conserved. b. Momentum is conserved, but kinetic energy is reduced. c. Momentum is not conserved, but kinetic energy is conserved. d. Neither momentum nor kinetic energy is conserved. e. Momentum is conserved, but the kinetic energy increases.

B

A high-jumper, having just cleared the bar, lands on an air mattress and comes to rest. Had she landed directly on the hard ground, her stopping time would have been much shorter. Using the impulse-momentum theorem as your guide, determine which one of the following statements is correct. a. The air mattress exerts the same impulse, but a greater net average force, on the high-jumper than does the hard ground. b. The air mattress exerts a greater impulse, but a smaller net average force, on the high-jumper than does the hard ground. c. The air mattress exerts the same impulse, but a smaller net average force, on the high-jumper than does the hard ground. d. The air mattress exerts a smaller impulse, and a smaller net average force, on the high-jumper than does the hard ground. e. The air mattress exerts a greater impulse, and a greater net average force, on the high-jumper than does the hard ground.

C

A projectile of mass 2.0 kg is shot straight up with an initial kinetic energy of 100 J. The system consists of the projectile and the Earth. If gravitational potential energy equals zero at the launching point, what is the potential energy of the system at maximum height ? Ignore air resistance. a. 0J b. 50J c. 100J d. 200J e. Not enough information is given.

C

A truck is traveling with a constant speed of 15 m/s. When the truck follows a curve in the road, its centripetal acceleration is 4.0 m/s2. What is the radius of the curve? a) 3.8 m b) 14 m c) 56 m d) 120 m e) 210 m

C

A wheel, originally rotating at 126 rad/s undergoes a constant angular acceleration of -5.00 rad/s2. What is its angular speed after it has turned through an angle of 628 radians? a. 121 rad/s b. 150 rad/s c. 98 rad/s d. 19 rad/s e. 15 rad/s

C

A wheel, originally rotating at 126 rad/s undergoes a constant angular deceleration of 5.00 rad/s2. What is its angular speed after it has turned through an angle of 628 radians? a. 121 rad/s b. 150 rad/s c. 98 rad/s d. 19 rad/s e. 15 rad/s

C

An airplane flying at 115 m/s due east makes a gradual turn while maintaining its speed and follows a circular path to fly south. The turn takes 15 seconds to complete. What is the radius of the circular path? a) 410 m b) 830 m c) 1100 m d) 1600 m e) 2200 m

C

An electric clock is hanging on a wall. As you are watching the second hand rotate, the clock's battery stops functioning, and the second hand comes to a halt over a brief period of time. Which one of the following statements correctly describes the angular velocity and the angular acceleration of the second hand as it slows down? a. W and A are both negative b. W is positive and A is negative c. W is negative and A is positive d. W and A are both positive

C

An object (mass = 4 kg) moves in space at a constant velocity of vi. There are no external forces acting on the object. The object then separates into two pieces, parts A and B, by a small explosive charge placed between them. After the explosion, part A has a mass of 1 kg and a velocity of +6 m/s, while part B has a mass of 3 kg and a velocity of +2 m/s. Parts A and B both move in the same direction after the explosion. What is the momentum of the 4-kg object before the explosion? a. 24 kgm/s b. 8 kgm/s c. 12 kgm/s d. 16 kgm/s e. Not enough information is given

C

Block A, with a mass of 2.0 kg, moves along the x axis with a velocity of 5 m/s in the positive x direction. It suffers an elastic collision with block B, initially at rest, and the blocks leave the collision along the x axis. If B is much more massive than A, the velocity of A after the collision is a. 0m/s b. +5 m/s c. -5 m/s d. +10 m/s e. -10 m/s

C

Figure 9-30 shows a snapshot of block 1 as it slides along an x axis on a frictionless floor, before it undergoes an elastic collision with stationary block 2. The figure also shows three possible positions of the center of mass (com) of the two- block system at the time of the snapshot. (Point B is halfway between the centers of the two blocks). Which statement describes the motion of block 1 after the collision if the com is located at point C? a. Block 1 is stationary b. Block 1 is moving forward c. Block 1 is moving backward d. Block 1 is either moving forward or backward.

C

Imagine you are swinging a bucket by the handle around in a circle that is nearly level with the ground (a horizontal circle). What is the force, the physical force on the bucket, holding the bucket in a circular path? a) the centripetal force b) the centrifugal force c) your hand on the handle d) gravitational force e) None of the above are correct.

C

In Fig. 8-33, a small block of mass m can slide along the frictionless loop-the-loop, with loop radius R. The block is released a point P, at height h = 5R. How much work is done by gravity when the block slides from P to Q? a. mgR b. 3mgR c. 4mgR d. 5mgR T e. None of the above

C

Two cars are traveling at the same constant speed v. As the drawing indicates, car A is moving along a straight section of the road, while car B is rounding a circular turn. Which statement is true about the accelerations of the cars? a. The acceleration of both cars is zero. b. Car A is accelerating, but car B is not. c. Car A is not accelerating, but car B is. d. Both cars are accelerating.

C

Two identical cars were involved in a collision at an icy intersection. Car A was stopped at a traffic light. Car B was moving at a speed v when it suffered a perfectly inelastic collision with the back end of car A. With what speed did the two cars slide into the intersection after the collision? a) 2v b) v c) v/2 d) v/4 e) v/8

C

Which one of the following is a characteristic of an inelastic collision? a. Total energy is not conserved. b. Linear momentum is not conserved c. Kinetic energy is not conserved d. The change in momentum is less than the total impulse. e. Total mass is not conserved.

C