Physics Exam 2

A 3.0-kg mass is located at (0.0 m, 8.0 m), and a 1.0-kg mass is located at (12 m, 0.0 m). You want to add a 4.0-kg mass so that the center of mass (or center of gravity) of the three-mass system will be at the origin. What should be the coordinates of the 4.0-kg mass? A) (3.0 m, 6.0 m) B) (-12 m, -8.0 m) C) (-3.0m,-6.0m) D) (-6.0 m, -3.0 m)

(-3.0m,-6.0m)

an object at rest begins to rotate with a constant angular acceleration. if this object rotates through an angle theta in time (t), through what angle did it rotate in time (1/2)t ?

(1/4)theta

A stone initially moving at 8.0 m/s on a level surface comes to rest due to friction after it travels 11 m. What is the coefficient of kinetic friction between the stone and the surface? A) 0.13 B) 0.25 C) 0.30 D) 0.43 E) 0.80

0.30

A wrench is used to tighten a nut as shown in the figure. A 12-N force is applied 7.0 cm from the axis of rotation. What is the magnitude of the torque due to the applied force?

0.84 n*m

A 35-N bucket of water is lifted vertically 3.0m and then returned to its original position. How much work did gravity do on the bucket during this process?

0J

what is the magnitude of the angular acceleration of the grindstone?

1.0 rad/s

Assuming for this calculation.. what is the recoil speed?

1.18x10^-5

A 14-kg beam is hinged at one end. A 6.0-kg triangular object and a 7.5-kg I-shaped object are positioned as shown. Dots indicate the individual centers of gravity of the beam and the two objects. What is the distance from the axis of rotation to the center of gravity for this system?

1.3 m

a 250kg motorcycle goes around an unbanked curve of radius 13.7m at a steady 96.5. what is the magnitude of the net force on the motorcycle?

1.31x10^4 N

a future use of space stations may be to provide hospitals... how long should each rotation take with a 200m radius to experience 1/10 the normal gravity on earth?

1.5 min

A 0.140 kg baseball is thrown with a velocity of 27.1 m/s. It is struck with an average force of 5000.0 N, which results in a velocity of 37.0 m/s in the opposite direction. How long was the bat and ball connected?

1.79x10^-3

Suppose our sun had 4 times its present mass but the earth orbited it at the same distance as it presently does. What would be the length of the year on the earth under those conditions?

1/2 as long as present year

A small but dense 2.0-kg stone is attached to one end of a very light rod that is 1.2 m long. The other end of the rod is attached to a frictionless pivot. The rod is raised until it is vertical, with the stone above the pivot. The rod is released and the stone moves in a vertical circle with no air resistance. What is the tension in the rod as the stone moves through the bottom of the circle? A) 20 N B) 40 N C) 60 N D) 80 N E) 100 N

100 N

what would be the weight of a 59.1kg astorunut on a planet with the same density as earth and having twice earths radius?

1160N

A force produces power by doing in a time. What power will be produced by a force that does six times as much work in Half as much time?

12P

a rubber band is stretched by 1.0 cm when a force of 0.35N is applied to each end. if instead a force of 0.70N is applied to each end, estimate how far the band will stretch

2.0 cm

What is the net power needed to change the speed of a 1600-kg sport utility vehicle from 15.0 m/s to 40.0 m/s in 4.00 seconds? A) 100 kW B) 10.0 kW C) 140 kW D) 14.0 kW E) 275 kW

275

an object attached to a spring is pulled across a horizontal frictionless surface. if the force constant of the spring is 45N/m and the spring us stretched by 0.88m when the object is accelerating at 1.4m/s what is the mass of the object?

28 kg

A 60-kg skier starts from rest from the top of a 50m high slope. if the work done by friction is -6.0kJ. what is the speed of the skier on reaching the bottom of the slope?

28 m/s

a 600kg car is going around a banked curve with a radius of 110m at a steady speed of 24.5. what is the banking angle so that the cars stays on its path without friction?

29.1

a car accelerates from rest to 30km/h. Later, on a highway it accelerates from 30 to 60. which takes more energy?

30 to 60

A spinning disc rotating at 130 rev/min slows and stops 31 s later. How many revolutions did the disc make during that time?

34

A proton of mass m is at rest when it is suddenly struck head-on by an alpha particle (which consists of 2 protons and 2 neutrons) moving at speed v. If the collision is perfectly elastic, what speed will the alpha particle have after the collision? (Assume the neutron's mass is equal to the proton's mass.) A) zero B) 2v/3 C) 3v/5 D) 5v/3

3v/5

If you want to double the momentum of a gas molecule, by what factor must you increase its kinetic energy?

4

when the speed of your car is doubled, by what factor does KE increase?

4

A ball attached to a string starts at rest and undergoes a constant angular acceleration as it travels in a horizontal circle with a radius of 0.30m. After 0.65sec the angular speed of the ball is 9.7 rad/s. what is the tangential acceleration of the ball?

4.5 m/s2

a car traveling at a velocity (v) can stop in a minimum distance (d). what would be the cars minimum stopping distance if it were traveling at a velocity of 2v?

4d

Two planets have the same surface gravity, but planet B has twice the radius of planet A. If planet A has mass m, what is the mass of planet B?

4m

A 1000-kg whale swims horizontally to the right at a speed of 6.0 m/s. It suddenly collides directly with a stationary seal of mass 200 kg. The seal grabs onto the whale and holds fast. What is the momentum of these two sea creatures just after their collision? You can neglect any drag effects of the water during the collision.

5.0 m/s

the drawing shows two 4.5 kg balls located on the y-axis... what is the location of the center of mass?

5.2m

which requires more work, increasing a cars speed from 0 to 30 or 50 to 60?

50 to 60

In a police ballistics test, a 2.00g bullet suddlenly hits and becomes embedded in a 5.0 kg wood block which is hanging from a 1.20m long string. this causes the block to swing through arc of 3.50. what was the speed of the bullet just before it hit the block?

524 m/s

The angular measure of 1.0 radian is equal to

57.3 degree

a 60kg woman stands on the very end of a uniform board of length l. which is supported one-quarter of the way from one end and is balanced. what is the mass of the board?

60kg

Jennifer is walking at 1.22 m/s. If Jennifer weighs 552 N, what is the magnitude of her momentum?

68.6kg * m/s

Three children are pulling on a rotatable platform on aplayground. The platform has a radius of 3.65 m. In thepicture, two children are pulling with equal forces of40.0 N in an attempt to make the platform rotateclockwise. The third child applies a force of 60 N asshown. What is the net torque on the platform?

76N*m CW

A jet plane flying 600 m/s experiences an acceleration of 4.0 g when pulling out of the circular section of a dive. What is the radius of curvature of this section of the dive?

9200m

a 0.065kg 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 15m/s. if the ball remains in contact with the racquet for .020s, what is the magnitude of the average force experienced by the ball?

98 N

Person X pushes twice as hard against a stationary brick wall as person Y. Which one of the following statements is correct?

Both do zero work

A heavy frog and a light frog jump straight up into the air. They push off in such away that they both have the same kinetic energy just as they leave the ground. Air resistance is negligible. Which of the following statements about these frogs are correct? (There could be more than one correct choice.)

Both frogs reach the same max height Just as they leave the ground the lighter frog is moving faster than the heavier frog

Two small balls, A and B, attract each other gravitationally with a force of magnitude F. If we now double both masses and the separation of the balls, what will now be the magnitude of the attractive force on each one?

F

a heavy ball suspended by a cable is pulled to the side by a horizontal force (f). if angle theta is small, the magnitude of the force can be less than the weight of the ball because

Force (f) is equal to only the x component of the tension in the cable

Halley's Comet is in a highly elliptical orbit around the sun. Therefore the orbital speed of Halley's Comet, while traveling around the sun,

Increases as it nears the sun

Which of the following are units of momentum?

N*s kg*m/s

Two cars go around a banked curve at the proper speed for the banking angle. One car has tires with excellent traction, while the other car has bald slippery tires. Which of these cars is more likely to slide on the pavement as it goes around the curve?

Neither car will slide

A spaceship is traveling to the moon. At which point is it beyond the pull of Earths gravity?

Never

A very elastic rubber ball is dropped from a certain height and hits the floor with a downward speed v. Since it is so elastic, the ball bounces back with the same speed v going upward. Which of the following statements about the bounce are correct?

The magnitude of the balls momentum was the same just before and just after the bounce

A small car meshes with a large truck in a head-on collision. Which of the following statements concerning the magnitude of the average collision force is correct?

The small car and truck experience the same average force

A rigid body rotates about a fixed axis with a constant angular acceleration. Which one of the following statements is true concerning the tangential acceleration of any point on the body?

The tangential acceleration depends on the change in the angular velocity

A person stands on the edge of a cliff. She throws threeidentical rocks with the same speed. Rock X is thrown verticallyupward, rock Y is thrown horizontally, and rock Z is thrownvertically downward. Assuming the elevation loss of the three rocksis the same (the base of the cliff is flat), which rock hits theground with the highest speed?

They all hit with the same speed

Two identical grasshoppers jump into the air with the same initial speed and experience no air resistance. Grasshopper A goes straight up, but grasshopper B goes up at a 66° angle above the horizontal. Which of the following statements about these grasshoppers are correct? (There could be more than one correct choice.

a.) At their highest point, both of them have the same amount of mechanical energy. b.) At their highest point, grasshopper B is moving faster than grasshopper A. e.)At their highest point, grasshopper A has more gravitational potential energy than grasshopper B.

which of the following point towards the center of the circle in a uniform circular motion? a. acceleration b. velocity, acceleration, net force c. velocity, acceleration d. velocity, net force e. acceleration, net force

acceleration, net force

a child whirls a ball in a vertical circle. assuming the speed of the ball is constant, when would the tension in the cord be the greatest? a. at the top of the circle b. at the bottom of the circle c. a little after the bottom d. a little before the bottom e. nowhere its equal at all points

at the bottom of the circle

a car drives at a steady speed around a perfectly circular track. a. the cars acceleration is zero b. the net force on the car is zero c. both acceleration and net force point outward d. both acceleration and net force point inward e. if there is no friction, the acceleration is outward

both acceleration and net force point inward

Two balls are thrown off a building with the same speed, one straight up and one at a 45 ∘ angle. Which statement is true if air resistance can be ignored?

both hit the ground with the same speed

Which pulls harder gravitationally, the Earth on the Moon, or the Moon on the Earth? Which accelerates more? a. the earth on the moon; the earth b. the earth on the moon; the moon c. the moon on the earth; the earth d. the moon on the earth; the moon e. both the same; the earth f. both the same; the moon

both the same; the moon

when you apply the torque equation to an object in equilibrium, the axis about which the torque is calculated...

can be located anywhere

When a net torque is applied to a rigid object, it always produces a

change in angular velocity

a small boat coasts at constant speed under a bridge. a heavy sack of sand is dropped from the bridge onto the boat. the speed will

decrease

a parking garage is designed for two levels of cars. to make more money, the owner decided to double the size in each dimension. for the support columns to hold up four floors instead of two, how should he change the columns diameter?

double the area of the columns by increasing their diameter by a factor of square root of 2

a ball is thrown straight up. at what point does the ball have the most energy? ignore air resistance

everywhere

in a rotating vertical cylinder, a rider finds herself pressed up against the wall. what is the correct free-body diagram of her. a. forces up, to the center, and down b. forces to and from the center and down c. forces to the center and down d. forces down to the center and kinda up e. forces up down and from the center

forces up, to the center, and down

Jill does twice as much work as Jack does and in half the time. Jill's power output is

four times as much as jacks

You push a heavy crate down a ramp at a constant velocity. Only four forces act on the crate. Which force does the greatest magnitude of work on the crate?

friction

Bonnie sits on the outer rim of a merry-go-round, and Jill sits midway between the center and the rim. The merry-go-round makes one complete revolution every 2 seconds. Jill's linear velocity is:

half of Bonnies

The momentum of an isolated system is conserved

in both elastic and inelastic collisions

If there were a great migration of people toward the Earth's equator, the length of the day would

increase because of conservation of angular mometum

a small mass (m) on a string is rotating without friction in a circle. the string is shortened by pulling It thru the axis of rotation without any external force torque. what happens to the angular velocity of the object?

it increases

a small mass (m) on a string is rotating without friction in a circle. the string is shortened by pulling It thru the axis of rotation without any external force torque. what happens to the tangential velocity of the object?

it increases

the moon does not crash into the earth because a. the net force on it is zero b. it is beyond the main pull of the earths gravity c. it is being pulled by the sun as well as the earth d. it is freely falling but it has a high tangential velocity

it is freely falling but it has a high tangential velocity

a space shuttle in orbit around the earth carries its payload with its mechanical arm. suddenly, the arm malfunctions and releases its payload. what will happen to the payload?

it will remain in the same orbit with the shuttle

A man pushes a block up an incline at a constant speed. As the block moves up the incline,

its PE increases and its KE remains the same

a railroad tank car contains milk and rolls at a constant speed along a level track. the milk begins to leak out of the bottom, the car then ...

maintains a constant speed

You are making a circular turn in your car on a horizontal road when you hit a big patch of ice, causing the force of friction between the tires and the road to become zero. While the car is on the ice, it

moves along a straight-line path in its OG direction

A woman is balancing on a high wire which is tightly strung as shown in Fig. 9-45. The tension in the wire is

much more than the womans weight

a uniform beam is hinged at one end and held in a horizontal position by a cable. the tension in the cable...

must be at least half the weight of the beam, no matter what angle of the cable

A baseball of mass m, initially at rest, is struck by a bat so that it acquires a speed v. If t represents the duration of the collision between the bat and the ball, which expression determines the magnitude of the average force exerted on the ball?

mv/t

A very light ping-pong ball moving east at a speed of 4 m/s collides with a very heavy stationary bowling ball. The Ping-Pong ball bounces back to the west, and the bowling ball moves very slowly to the east. Which object experiences the greater magnitude impulse during the collision?

neither; both experienced the same magnitude impulse

two identical billiard balls traveling at the same speed have a head on collision and rebound. if the balls had twice the mass but maintained the same size and speed, how would the rebound be different?

no difference

a bowling ball is dropped from a height (h) onto the center of a trampoline which launches the ball back up into the air. how high will the ball rise?

no more than h- probably a little less

A satellite in circular orbit around the Earth moves at constant speed. This orbit is maintained by the force of gravity between the Earth and the satellite, yet no work is done on the satellite. How is this possible?

no work is done if the direction of motion is perpendicular to the forces

You push very hard on a heavy desk, trying to move it. You do work on the desk:

only if it starts moving

An egg falls from a bird's nest in a tree and feels no effects due to the air. As it falls,

only its mechanical energy is conserved

the space shuttle in circular orbit around the earth collides with a small Astroid which ends up in the shuttles storage bay, for this collision..

only momentum is conserved

a car goes around circular curve on a horizontal road at a constant speed. What is the direction of the friction force on the car due to the road?

perpendicular to the curve inward

two children are balanced on opposite sides of the seesaw. if one child leans inward toward the center pivot point, her side will

rise

If you used 1000 J of energy to throw a ball, would it travel faster if you threw the ball (ignoring air resistance)

so that it wasn't rotating

suppose you are sitting on a rotating stool holding a 2 kg mass in each outstretched hand. if you suddenly drop the masses, your angular velocity will

stay the same

a ping-pong ball is shot into a circular tube that is lying flat on a tabletop. when the ping-pong ball exits the tube, which path will it follow? a. up b. sorta up c. straight d. sorta down e. down

straight out

two objects constitute an isolated system. if an elastic collision between two objects, which statement is FALSE?

the KE of each object is the same before and after the collision

a ball is thrown straight up. neglecting air resistance, which statement is NOT true regarding the energy of the ball?

the PE decreases while the ball is going up

in the international space station, which orbits Earth, astronauts experience apparent weightlessness because

the astronauts and the space station are in free fall towards the center of the earth

a bowling ball hangs from a 1.0m long cord. (1) a 200 gram putty ball moving 5.0m/s hits the bowling ball and sticks to it causing the bowling ball to swing up. (2) in a 200 gram rubber ball moving 5.0m/s hits the bowling ball and bounces straight back at nearly 5.0m/s causing the bowling ball to swing up. describe what happens.

the ball swings further in 2 than in 1

A baseball is pitched horizontally toward home plate with a velocity of 110 km/h. In which of the following scenarios does the baseball have the largest change in momentum?

the baseball is hit straight back to the pitcher at 110 km/h

A hollow cylinder of mass M and radius R rolls down an inclined plane. A block of mass M easily slides down an identical inclined plane. Complete the following statement: If both objects are released at the same time from the top of their inclined planes, A) the cylinder will reach the bottom first. B) the block will reach the bottom first. C) the block will reach the bottom with the greater kinetic energy. D) the cylinder will reach the bottom with the greater kinetic energy. E) both the block and the cylinder will reach the bottom at the same time.

the block will reach the bottom first

while driving fast around a sharp right turn, you find yourself pressing against the car door. What is happening? a. centrifugal force is pushing you into the door b. the door is exerting a rightward force on you c. both d. neither

the door is exerting a rightward force on you

Consider two less-than-desirable options. In the first you are driving 30 mph and crash head-on into an identical car also going 30 mph. In the second option you are driving 30 mph and crash head-on into a stationary brick wall. In neither case does your car bounce back from the thing it hits, and the collision time is the same in both cases. Which of these two situations would result in the greater impact force on your car?

the force would be the same in both cases

A golf ball and an equal-mass bean bag are dropped from the same height and hit the ground. The bean bag stays on the ground while the golf ball rebounds. Which experiences the greater impulse from the ground?

the golf ball

Two spheres have the same radius and equal masses. One is made of solid and the other is hollow and made of denser material. which one has the bigger moment of inertia about an axis thru the center?

the hollow one

A small solid sphere and a small thin hoop are rolling along a horizontal surface with the same translational speed when they encounter a 20 ∘ rising slope. if these two objects roll up the slope without slipping, which will rise further up the slope?

the hoop

Engines, including car engines, are rated in horsepower. What is horsepower?

the rate at which the engine can do work

a rock is dropped from a high tower and falls freely under the influence of gravity. which one of the statements about the rock is true?

the rock will gain equal amounts of momentum during each second

A solid sphere and a hollow sphere each of mass M and radius R are released at the same time from the top of an inclined plane. Which one of the following statements is necessarily true?

the solid sphere will reach the bottom first

You are lying in bed and you want to shut your bedroom door. You have a superball and a blob of clay (both with the same mass) sitting next to you. Which one would be more effective to throw at your door to close it?

the super ball

a 10.0N weight is suspended by two cords as shown, what can you say about the tension in the two cords?

the tension in the shorter cord, is greater than in the longer cord

Two satellites orbit the Earth in circular orbits of the same radius. One satellite is twice as massive as the other. Which statement is true about the speeds of these satellites?

the two satellites have the same speed

Two wheels having the same radius and mass rotate at the same angular velocity. One wheel is made with spokes so nearly all the mass is at the rim. The other is a solid disk. How do their rotational kinetic energies compare?

the wheel with the spokes has about twice the KE

as you increase the force that you apply while pulling on a rope, which of the following is not affected?

the young modulus of the rope

a truck going 15 km/h has a head on collision with a small car going 30 km/h. which statement best describes the situation?

they both have the same change in magnitude of momentum because momentum is conserved

A small car and a heavy pickup truck are both out of gas. The truck has twice the mass of the car. After you push both the car and the truck for the same amount of time with the same force, what can you say about the momentum and kinetic energy of the car and the truck? Ignore friction.

they have the same momentum but the car has more KE than the truck

An astronaut is a short distance away from her space station without a tether rope. She has a large wrench. What should she do with the wrench to move toward the space station?

throw it directly away from the space station

a collision is elastic if...

total kinetic energy is conserved

A car speedometer that is supposed to read the linear speed of the car uses a device that actually measures the angular speed of the tires. If larger-diameter tires are mounted on the car instead, how will that affect the speedometer reading? The speedometer

will read low

What is the instantaneous speed of the object making contact with the surface?

zero