Physics Exam 2
If you were standing on a cart that was at rest and free to roll (ignore friction) and someone threw a 10 kg ball at you, you would A. not move if you caught the ball because you are more massive than the ball. B. roll backward faster if you caught the ball. C. roll backward faster if the ball bounced off of you elastically. D. roll backward faster if you caught the ball higher above the ground.
C. roll backward faster if the ball bounced off of you elastically.
As shown in the figure, a bullet of mass 0.010 kg moving horizontally suddenly strikes a block of wood of mass 1.5 kg that is suspended as a pendulum. The bullet lodges in the wood, and together they swing upward a vertical distance of 0.40 m. The length of the string is 2.0 m. What was the speed of the bullet just before it struck the wooden block? A) 67 m/s B) 250 m/s C) 370 m/s D) 420 m/s E) 650 m/s
D) 420 m/s
Force F, acting for time T and over a distance D, gives impulse I. To get the same impulse using half the force, it would be necessary for the force to act A. over a distance 2D. B. over a distance 4D. C. over half the distance D. D. for a time 2T. E. for half the time T.
D. for a time 2T.
A car moving east collides with a truck moving north. The vehicles have the same speed but the truck has twice the mass of the car. If the vehicles stick together after the collision, what is the path followed by the vehicles after the collision? A B C D E
B
In attempting to pull a 1500-kg car out of a ditch, Al exerts a force of 200 N for 5 s, Bill exerts a force of 500 N for two s, and Clyde exerts a force of 300 N for four seconds. The car does not move at all. Who provided the greatest impulse? A. Arnold B. Bob C. Cecil D. They all provide equal impulse on the car
C. Cecil
A steady horizontal force lasting 2.10s give a 1.25kg object an acceleration of 3.20 m/s2 on a frictionless table. What impulse does this force give to the object? a) 8.40 kg m/s b) 2.62 kg m/s c) 10.9 kg m/s d) 4.00 kg m/s e) 25.7 kg m/s
J = F * t = m * a * t = 1.25 * 3.20 * 2.10 = 8.4 N-s A
A 0.140kg baseball is thrown with a velocity of . It is struck with an average force of 5000N, which results in a velocity of in the opposite direction. How long were the bat and ball in contact? a) 3.17x 10^-2s b) 4.44 x 10^-3s c) 1.85 x 10^-3s d) 1.32 x 10^-2s
Need values
A car of mass 1,411kg collides head-on with a parked truck of mass 2000kg. Spring mounted bumpers ensure that the collision is essentially elastic. If the velocity of the truck is 17km/h (in the same direction as the car's initial velocity) after the collision, what is the initial speed of the car? a) 21 km/h b) 32 km/h c) 42 km/h d) 11 km/h
Unsure, possibly 11 km/h
A bullet of mass 0.010 kg and speed of 100 m/s is brought to rest in a wooden block after penetrating a distance of 0.10 m. The work done on the bullet by the block is a) 1.0 Ns b) zero c) 4.0 Ns d) 0.98 N e) 2.0 Ns
a) 1.0 Ns
A golf ball of mass 0.050 kg is at rest on the tee. Just after being struck, it has a velocity of 102 m/s. If the club and ball were in contact for 0.81 ms, what is the average force exerted on the ball by the club? a) 6.3 kN b) 7.1 kN c) 4.9 kN d) 5.5 kN
a) 6.3 kN Impulse causes the change in momentum in time, Δt = 0.81×10−3 s Δp = mv f − 0 = (0.050)(102) Ns = 5.10 Ns Impulse: FΔt = Δp; F = Δp Δt =(5.10 / 0.81×10−3 )N = 6.30kN
A 1200 kg cart is rolling at 10.8 m/s across a flat surface. A crane dumps 852 kg of one (Vertically) into the cart. How fast does the cart move after being loaded with ore? Assume that frictional forces with the flat surface may be neglected. a) 6.3 m/s b) 4.2 m/s c) 3.8 m/s d) 5.7 m/s
a) 6.3 m/s
You are standing on a skateboard, initially at rest. A friend throws a very heavy ball towards you. You have two choices about what to do with the ball: either catch the ball or deflect it back toward your friend with the same speed as it was originally thrown. Which choice should you make in order to maximize your speed on the skateboard? a) Deflect the ball back b) Catch the ball c) Your final speed on the skateboard with be the same regardless of whether you catch the ball or deflect the ball
a) Deflect the ball back
In an Inelastic collision involving an isolated system, the final total momentum is a) Exactly the same as the initial momentum b) more than the initial momentum c) less than the initial momentum
a) Exactly the same as the initial momentum
An egg falls from a bird's nest in a tree and feels no effects due to the air. As it falls a) Only its mechanical energy is conserved b) Both its mechanical energy and its momentum are conserved c) Both its kinetic energy and its momentum are conserved d) Only its momentum is conserved e) only its kinetic energy is conserved
a) Only its mechanical energy is conserved
A firecracker explodes in midair and breaks up into many fragments. Which of the following statements are true regarding conditions immediately before and immediately after the explosion: I: The total momentum of the fragments is equal to the original momentum of the firecracker. II: The total kinetic energy of the fragments is equal to the original kinetic energy of the firecracker. a) Statement I only b) Statement II only c) Both Statement I and Statement II d) Neither statement is true
a) Statement I only
A toy car and a toy truck at rest have a compressed spring in between them. The truck has more mass than the car. The spring is released and the two cars move in opposite directions. Which of the following is true? a) The magnitude of the truck's momentum is the same as the car's. b) The magnitude of the truck's momentum is larger than the car's. c) The magnitude of the truck's momentum is smaller than the car's. d) It is not possible to tell which has more momentum without knowing the speeds.
a) The magnitude of the truck's momentum is the same as the car's.
A car meshes with a large truck in a head-on collision. Which of the following statements concerning the magnitude of the momentum change during the collision is correct? (There could be more than one correct choice.) a) The small car and the truck experience the same magnitude momentum change b) The magnitude of the momentum change experienced by each one is inversely proportional to its mass c) The truck experiences the great magnitude momentum change d) The small car experiences the greater magnitude momentum change e) The magnitude of the momentum change experienced by each one is directly proportional to its mass
a) The small car and the truck experience the same magnitude momentum change
A tennis ball bounces off a brick wall. Which of the following is true? a) The total momentum of the ball, wall, and Earth is conserved in this process b) If the collision is elastic, then the ball's velocity does not change in this process c) The momentum of the ball is conserved in this process d) None of these choices are true
a) The total momentum of the ball, wall, and Earth is conserved in this process
During World War I, Germany used a "Big Bertha" cannon to hurl shells into Paris 30 miles away. This gun also had a long barrel. What is the reason for using a long barrel in these guns? a) To allow the force of the expanding gases from the gunpowder to act for a longer time b) To reduce the force exerted on the bullet due to the expanding gases from the gunpowder c) To provide a larger ratio of Kinetic Energy to Potential Energy d) To increase the force exerted on the bullet due to the expanding gases from the gunpowder e) To reduce frictional losses
a) To allow the force of the expanding gases from the gunpowder to act for a longer time
Two people sit face to face on skateboards that are free to roll w/o friction. They push each other with a force of 40 N and move apart. Person X whose mass is 50 kg, moves to the left at 3 m/s. Person Z whose mass is 60 kg is a) moves to the right at 2.5 m/s b) moves to the right at 10 m/s c) moves to the right at 4 m/s d) moves to the right at 1 m/s
a) moves to the right at 2.5 m/s
In the figure, determine the character of the collision. The masses of the blocks, and the velocities before and after, are shown. The collision is a) perfectly elastic b) partially inelastic c) completely inelastic d) characterized by an increase in kinetic energy e) not possible because momentum is not conserved
a) perfectly elastic
If you want to double the kinetic energy of a gas molecule, by what factor must you increase its momentum? a) square root of 2 b) 4 c) 16 d) 2 e) 2 * square root of 2
a) square root of 2
Two object of different masses have equal, non-zero kinetic energies. Which object has the greater magnitude momentum? a) the heavier object b) the lighter object c) They both have the same magnitude momentum
a) the heavier object
A 2.0 kg ball moving eastward at 3.0 m/s suddenly collides with and sticks to a 4.0 g ball moving northward at 2.0 m/s. What is the magnitude of the momentum of this system just after the collision? a) 2.0 kg * m/s b) 6.0 kg * m/s c) 14 kg * m/s d) 10 kg * m/s e) 8.0 kg * m/s
d) 10 kg * m/s
When a baseball hits the ball, the impulse delivered to the ball is increased by a) rapidly stopping the bat after impact b) "follow through" on the swing, which increases contact time c) the impulse cannot be changed d) letting the bat recoil upon impact
b) "follow through" on the swing, which increases contact time
An oil tanker heading due west, straight into a strong wind, reaches a speed of 5 m/s and then shuts down its engines to drift. The forward-facing flat surfaces of the tanker catch a total of 60,000 N of force from the wind. This wind force is pointing backwards, to the east. The tanker's mass is 100,000 metric tons, which is 100 million kg. If the wind blows at the same strength for 5 minutes, then how much has the wind changed the tanker's speed? a) 0.018 m/s b) 0.18 m/s c) 1.08 m/s d) 1.2 m/s
b) 0.18 m/s
A 0.14kg baseball is dropped from rest from a height of 2.0m above the ground. What is the magnitude of its momentum just before it hits the ground if we neglect air resistance? a) 0.44 kg * m/s b) 0.88 kg * m/s c) 0.62 kg * m/s d) 1.4 kg * m/s e) 0.28 kg * m/s
b) 0.88 kg * m/s
A 2.0kg mass moving at 5.0 m/s suddenly collides head-on with a 3.0kg mass at rest. If the collision is perfectly inelastic, what is the speed of the masses just after the collision? a) 2.5 m/s b) 2.0 m/s c) 10 m/s d) 0 m/s, since the collision is inelastic
b) 2.0 m/s
If the speed of a car is tripled, the impulse required to stop the car changes by a factor of a) 9 b) 3 c) 1/9 d) 1/3 e) 1
b) 3
Moving at a constant speed, an elevator lifts a 1000 N package 10 m in 3 seconds. During this time, the impulse delivered to the package by the elevator floor is a) 10,000 Nm up b) 3,000 Ns up c) 10,000 Ns up d) zero
b) 3,000 Ns up
A tiger is running in a straight line. If we double both the mass and speed of the tiger, the magnitude of its momentum will increase by what factor? a) 16 b) 4 c) 0 d) 8 e) 2
b) 4
If you want to double the momentum of a gas molecule, by what factor must you increase its kinetic energy? a) square root of 2 b) 4 c) 16 d) 2 e) 2 * square root of 2
b) 4
A super dart of mass 20g, traveling at 350 m/s, strikes a steel plate at an angle of 30° with the plane of the plate, as shown in the figure. It bounces off the plate at the same angle but at a speed of 320 m/s. What is the magnitude of the impulse that the plate gives to the bullet? a) 0.30 N*s b) 6.7 N*s c) 0.52 N*s d) 300 N*s e) 4.3 N*s
b) 6.7 N*s
A 1200kg car moving at 15.6m/s collides with a stationary car of mass 1500kg. If the two vehicles lock together, what is their combined velocity immediately after the collision? a) 8.6 m/s b) 6.9 m/s c) 5.5 m/s d) 12.1 m/s
b) 6.9 m/s
An 83g steel ball is released from rest and falls vertically onto a steel plate. The ball strikes the plate and is in contact with it for 0.5ms. The ball rebounds elastically, and returns to its original height. The time interval for a round trip is 4.00s. In this situation, assume the plate does not deform during contact. The maximum elastic energy stored by the ball is closest to: a) 24 J b) 64 J c) 32 J d) 48 J e) 16 J
b) 64 J
There must be equal amounts of mass on both sides of the center of mass (or center of gravity) of a system. a) True b) False
b) False
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? a) the Ping-Pong ball b) Neither, both experienced the same magnitude impulse c) It is impossible to tell since the actual mass values are not given d) It is impossible to tell since the velocities after the collision are unknown e) the bowling ball
b) Neither, both experienced the same magnitude impulse
Suppose you are out on a frozen lake, where there is no friction. Which of the following would start you moving towards the shore? a) Removing a shoe and throwing it towards the shore b) Removing a shoe and throwing it away from the shore c) Shouting a someone on the shore d) None of these choices would work
b) Removing a shoe and throwing it away from the shore
Two friends are standing on opposite ends of a canoe that is initially at rest with respect to a frictionless lake. The person in the front throws a very massive ball toward the back, and the person in the back catches it. After the ball is caught, the canoe is a) Moving Backwards b) Stationary c) Moving Forward
b) Stationary
A 5kg ball collides inelastically head-on with a 10kg ball, which is initially stationary. Which of the following statements is true? (There could be more than one correct choice.) a) The magnitude of the change of velocity the 5kg ball experiences is equal to that of the 10kg ball b) The magnitude of change of velocity the 5kg ball experiences is greater than that of the 10kg ball c) The magnitude of change of velocity the 5kg ball experiences is less than that of the 10kg ball d) The magnitude of the change of momentum of the 5kg ball is equal to the magnitude of the change of momentum of the 10kg ball e) Both balls lose all their momentum since the collision is inelastic
b) The magnitude of change of velocity the 5kg ball experiences is greater than that of the 10kg ball d) The magnitude of the change of momentum of the 5kg ball is equal to the magnitude of the change of momentum of the 10kg ball
A car meshes with a large truck in a head-on collision. Which of the following statements concerning the momentum during the collision are correct? (There could be be more than one correct choice.) a) The momentum of the truck is conserved b) The momentum of the car-truck system is conserved, but the momentum of each one is not conserved c) The momentum of the car and the momentum of the truck are each conserved d) The car and the truck must undergo the same change in speed e) The momentum of the car is conserved
b) The momentum of the car-truck system is conserved, but the momentum of each one is not conserved
Three cars, car X, car Y, and car Z, begin accelerating from rest at the same time. Car X is more massive than car Y, which is more massive than car Z. The net accelerating force exerted on each car is identical. After 10 seconds, which car has the most amount of momentum? a) Car Z b) They all have the same amount of momentum c) Car Y d) Car X
b) They all have the same amount of momentum
A box is pushed eastward across a rough horizontal floor by a force acting parallel to the floor. A force providing an impulse directed westward on the body is a) normal reaction force of floor upward on body b) friction c) the applied force d) gravity e) a fictitious force
b) friction
Which of the following quantities are units of impulse? (There could be more than one correct choice) a) kg * m^2/s^2 b) kg * m/s c) kg * s/m d) N * m e) N * s
b) kg * m/s e) N * s
Which of the following quantities are units of momentum? (There could be more than one correct choice) a) kg * m^2/s^2 b) kg * m/s c) kg * s/m d) N * m e) N * s
b) kg * m/s e) N * s
The ping-pong ball is dropped vertically onto a stationary bowling ball resting on the floor. Which of the balls experiences the greater force as a result of the collision? a) the ping-pong ball b) neither, both experience forces of the same size c) the bowling ball d) it's impossible to tell from this data
b) neither, both experience forces of the same size
A rubber ball bounces off a wall with an initial speed v and reverses its direction so its speed is v right after the bounce. As a result of this bounce, which of the following quantities of the ball are conserved? (There could be more than one correct choice.) a) both the momentum and the kinetic energy of the ball b) the kinetic energy of the ball c) the momentum of the ball d) None of the above quantities are conserved
b) the kinetic energy of the ball
Two object of different masses have momentum of equal, non-zero magnitude. Which object has more kinetic energy? a) the heavier object b) the lighter object c) They both have the same Kinetic energy
b) the lighter object
Consider a system containing three objects that move with different velocities. The objects can interact with each other through forces. In this system a) the total kinetic energy of the objects will not change unless an outside force is applied b) the total momentum of the objects cannot change unless an outside force acts on the system c) the objects can only collide if an outside force is applied d) any collisions between the objects must be elastic
b) the total momentum of the objects cannot change unless an outside force acts on the system
A block of mass m = 3.6 kg, moving on a frictionless surface with a speed of vi = 9.3 m/s, makes a sudden perfectly elastic collision with a stationary block of mass M, as shown in the figure. Just after the collision, the 3.6-kg block recoils with a speed of vf = 2.7 m/s. What is the speed V of the other block? A) 6.6 m/s B) 8.0 m/s C) 9.3 m/s D) 10.7 m/s E) 12.0 m/s
by conservation of momentum we have mu= -mv+MVm = 3.6u = 9.3v = 2.7V = 43.2/M by conservation of energy we have. 5mu2 = 0.5mv2+0.5MV2 by solving the eqns we get A) V=6.6m/s
Three objects are moving along a straight line as shown in the figure. Taking the positive direction to be to the right, what is the total momentum of this system? a) 0.00 kg m/s b) +14.0 kg m/s c) -14.o kg m/s d) +106 kg m/s e) -106 kg m/s
c) -14.o kg m/s
A 30 kg child runs at 3.0 m/s and jumps onto a shopping cart and holds on for dear life. The cart has a mass of 20 kg. Assuming the child rides on the cart after the collision, the speed of the child and shopping cart just after the child jumps on is a) 2.5 m/s b) zero c) 1.8 m/s d) 3.0 m/s
c) 1.8 m/s
A car heading north collides at an intersection with a truck heading east. If they lock together and travel at 28m/s at 15° north of east just after the collision, how fast was the car initially traveling? Assume that the two vehicles have the same mass. a) 28 m/s b) 11 m/s c) 14 m/s d) 7 m/s
c) 14 m/s
Two vehicles approach a right-angle intersection and then collide. After the collision, they become entangled. If their mass ratios were 1:4 and their respective speeds as they approached were both 13 m/s, find the magnitude and direction of the final velocity of the wreck. a) 13.1 m/s at 79° b) 12.5 m/s at 75° c) 15.7 m/s at 79° d) 16.3 m/s at 79°
c) 15.7 m/s at 79°
An 80 kg football player travels to the right at 8 m/s and a 120 kg player on the opposite team travels to the left at 4.0 m/s. the total momentum is a) 1120 kg m/s to the right b) zero c) 160 kg m/s to the left d) 240 kg m/s to the left e) 160 kg m/s to the right
c) 160 kg m/s to the left (80x 8)-(120x4)= 160 kg
A child runs at 3.0 m/s and jumps onto a sled, initially at rest. If the child's mass is 36 kg, and if the child and sled slide off together at 2.0 m/s after the collision, the sled's mass is a) 48 kg b) 36 kg c) 18 kg d) 12 kg
c) 18 kg
A 1200 kg cannon fires a 100.0 kg cannonball at 35m/s. What is the recoil velocity of the cannon? Assume that frictional forces are negligible and the cannon is fired horizontally. a) 3.2 m/s b) 3.5 m/s c) 2.9 m/s d) 35 m/s
c) 2.9 m/s 1200kg∗v(recoil)[bd] = 100.0kg∗35m/s[fd]1200kg∗v(recoil)[bd] = 100.0kg∗35m/s[fd] Now rearrange to get: v(recoil)=2.916777...m/s[bd]
A block of mass m = 5.6 kg, moving on a frictionless surface with a velocity of vi = 6.5 m/s to the right, collides with a block of mass M at rest, as shown in the figure. After the collision, the 5.6 kg block recoils with a velocity of vf = 0.70 m/s to the left. If the blocks are in contact for 0.20 s, what is the magnitude of the average force on the 5.6 kg block, while the two blocks are in contact? a) 192 N b) 0 N c) 202 N d) 182 N e) 0 N
c) 202 N I1 = F1t = Δp1 = m1v1f - m1v1i = m1(v1f - v1i) F1 = m1(v1f - v1i)/t = (5.6)(-0.70 - 6.5)/0.20 N = -201.6 N [points left]
A block of mass m = 34kg and speed V is behind a block of mass M = 81kg and speed of 0.50 m/s as shown in the figure. The surface is frictionless and the blocks collide and couple. After the collision, the blocks have a common speed of 0.90m/s. What is the magnitude of the impulse on the 34kg block due to the collision? a) 73 N*s b) 14 N*s c) 32 N*s d) 57 N*s e) 41 N*s
c) 32 N*s
A 3 kg block, initially moving due east at 6 m/s, is acted upon by an impulse having magnitude 6 N·s and direction due west. The final velocity of the block is a) 8 m/s east b) 4 m/s west c) 4 m/s east d) 8 m/s west
c) 4 m/s east
A 0.24kg blob of clay is thrown at a wall with an initial velocity of 16 m/s. If the clay comes to a stop in 91ms, what is the average force experienced by the clay? a) 35 N b) 26 N c) 42 N d) 51 N
c) 42 N F/t = ma/t = (0.24kg*16m/s)/.091s = 42N
A block of m = 9.0 kg and speed V and is behind a block of mass M = 27kg and speed of 0.50 m/s, as shown in the figure. The surface is frictionless, and the blocks suddenly collide and couple. After the collision, the blocks have a common speed of 0.90 m/s. How much kinetic energy of the blocks is lost due to the collision? a) 4.6 J b) 2.0 J c) 8.6 J d) 31 J e) 11 J
c) 8.6 J
A girl of mass 55kg throws a ball of mass 0.8kg against a wall. The ball strikes the wall horizontally with a speed 25 m/s of and it bounces back with this same speed. The ball is in contact with the wall 0.05s. What is the average force exerted on the wall by the ball? a) 27,500 N b) 400 N c) 800 N d) 55,000 N e) 13,750 N
c) 800 N
Object A moving due east collides with object B moving due west. After the collision, A is moving 20° north of due east. What must be true of B after the collision? a) At least part of B's velocity must be toward the west b) B must be moving 20° south of due east c) At least part of B's velocity must be toward the south d) B must be moving 20° south of due west e) None of these choices are true
c) At least part of B's velocity must be toward the south
The momentum of an isolated system is conserved a) Only in elastic collisions b) Only in inelastic collisions c) In both elastic and inelastic collisions
c) In both elastic and inelastic collisions
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 upwards. Which of the following statements about the bounce are correct? (There could be more than one correct choice.) a) The ball's momentum was conserved during the bounce b) The magnitude of the ball's momentum was the same just before and just after the bounce c) The ball had the same momentum just before and just after the bounce d) None of the above statements are correct
c) The ball had the same momentum just before and just after the bounce
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? a) Hitting the other car b) None of the above choices are correct c) The force would be the same in both cases d) Hitting the brick wall
c) The force would be the same in both cases
A rocket explodes into two fragments, one 25 times heavier than the other. The magnitude of the momentum change of the lighter fragment is a) 25 times as great as the momentum change of the heavier fragment b) 1/25 as great as the momentum change of the heavier fragment c) The same as the momentum change of the heavier fragment d) 5 times as great as the momentum change of the heavier fragment e) 1/4 as great as the momentum change of the heavier fragment
c) The same as the momentum change of the heavier fragment
Suppose a ball is dropped from should height, falls, makes a perfectly elastic collision with the floor, and rebound to shoulder height. Compare the magnitudes of the impulses delivered to the ball by the gravity and by the floor during this entire motion a) The impulse delivered by the floor is half as large as the impulse delivered by gravity b) The floor delivers an upward impulse, but gravity does not deliver a total impulse c) The two impulses have the same magnitude d) The impulse delivered by the floor is twice as large as the impulse delivered by gravity
c) The two impulses have the same magnitude
In a collision between two unequal masses, which mass receives a greater magnitude impulse? a) the larger mass b) the smaller mass c) They receive equal impulses
c) They receive equal impulses
A racquetball is dropped from a height of one meter. It bounces off the floor and rises to a height of 0.8 m. The collision with the floor was a) an elastic collision b) a perfectly inelastic collision c) a partially inelastic collision d) impossible to tell without knowing the mass of the ball
c) a partially inelastic collision
In the game of pool, the white cue ball hits the #5 ball and stops, while the #5 ball moves away with the same velocity as the cue ball had originally. Both balls have the same mass. This type of collision is a) Somewhat inelastic b) Completely inelastic c) elastic
c) elastic
On a horizontal frictionless air table, a puck runs into an ideal horizontal spring that is fastened to the table. The puck compresses the spring by 15 cm before coming to rest. During the compression process, which quantities are conserved? a) the momentum and the kinetic energy of the puck b) only the momentum of the puck c) only the mechanical energy (kinetic plus potential) of the puck d) the momentum and the mechanical energy of the puck e) only the kinetic energy of the puck
c) only the mechanical energy (kinetic plus potential) of the puck
A gun is made of a super-low-weight but strong material. The bullet for the gun is more massive than the gun itself. For such a gun a) conservation of momentum is not satisfied b) recoil problems would be lessened c) the gun, if unsupported, would have a recoil velocity higher than the bullet velocity d) the bullet would go faster with less powder
c) the gun, if unsupported, would have a recoil velocity higher than the bullet velocity
A friend drops a package to you from a window 16 feet above where you first catch it. It drops an additional 3 feet as you bring it to a stop with a constant force. In order to calculate the force required, you need a) no additional information b) the time it takes for you to stop the package c) the mass of the package
c) the mass of the package
If a single force acts on a moving object a) the momentum of the object can only change direction, not magnitude b) the momentum of the object will change only if the force is in the same direction as the velocity of the object c) the momentum of the object must change d) the momentum of the object can only change magnitude, not direction
c) the momentum of the object must change
Two pendulums of equal length l = 0.45m are suspended from the same point. The pendulum bobs are steel spheres. The first bob is drawn back to make a 35° angle with the vertical. If the first Bob has mass 0.25kg and the second has mass 0.85kg, how high will the second Bob rise above its initial position when struck elastically by the first Bob after it is released? a) 3.9cm b) 3.3cm c) 4.4cm d) 2.7cm
d) 2.7cm First bob has height h = L(1 - cosΘ) = 0.45m * (1 - cos35º) = 0.0814 m and so arrives at the impact point with velocity V = √(2gh) = √(2 * 9.8m/s² * 0.0814m) = 1.263 m/s For an elastic, head-on collision, we know (from CoE) that the relative velocity of approach = relative velocity of separation, or V = 1.263m/s = v - u → for u, v the post-collision velocities of 0.25kg, 0.63kg bob So u = v - 1.263m/s Now conserve momentum: initial mv = Σ final mv 0.25kg * V = 0.25kg * u + 0.63kg * v 0.25 * 1.263 = 0.25(v - 1.263) + 0.63*v = 0.88v - 0.316 v = 0.631 / 0.88 = 0.718 m/s Then h' = v² / 2g = (0.718m/s)² / 19.6m/s² = 0.026 m = 2.6 cm
In a head-on automobile collision, a person's momentum could be reduced from 2000 kg m/s to zero in just 0.1 s. If this occurs, the average force exerted to stop the person is a) Can't answer without knowing the person's mass. b) 200 N. c) 2,000 N. d) 20,000 N.
d) 20,000 N.
A 51g steel ball is released from rest and falls vertically onto a steel plate. The ball strikes the plate and is in contact with it for 0.5 ms. The ball rebounds elastically, and returns to its original height. The time interval for a round trip is 3.00s. In this situation, the average force exerted on the ball during contact with the plate is closest to: a) 2490 N b) 2000 N c) 1500 N d) 3000 N e) 3500 N
d) 3000 N
An object initially at rest explodes in two fragments of masses 5kg and 7.5kg that move in diametrically opposite directions. If the speed of the first fragment is 8.1 m/s, find the internal energy of the explosion. a) 30J b) 38J c) 38kJ d) 30kJ
d) 30kJ (Ma+Mb)•u = Ma•-Va + Mb•Vb 0 = —5 × 8.1 + 7.5Vb 0 = —40.5 + 7.5Vb 7.5Vb = 40.5 Vb = 40.5/7.5 Vb = 5.4m/s Total kinetic energy of the fragment is equal to energy of explosion K.E = ½Ma•Va² + ½Mb•Vb² K.E = ½ × 5 × 8.1² + ½ × 7.5 × 5.4² K.E = 164.025 + 109.35 K.E = 273.375 J
During a collision, which of these is an indication that the total kinetic energy has changed? a) Sound is produced b) Deformation occurs c) Heat is generated d) All of these choices are indication that the kinetic energy has changed e) None of these choices are correct
d) All of these choices are indication that the kinetic energy has changed
A painter of mass 80 kg climbs 3.0 m up a ladder. The painter has gained momentum in the amount of a) 240 J b) 2352 J c) 784 J d) Can't say without knowing his velocity change (if any)
d) Can't say without knowing his velocity change (if any)
Identical forces act for the same length of time on two different objects. The magnitude of the change in momentum of the lighter object is a) Smaller than the magnitude of the change in momentum of the large mass, but not zero b) Zero c) There is not enough information to answer the question d) Exactly equal to the magnitude of the change in momentum of the larger mass e) Larger than the magnitude of the change of momentum of the larger mass
d) Exactly equal to the magnitude of the change in momentum of the larger mass
A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force providing no impulse during the motion is a) friction b) the applied force c) gravity d) None of these choices are correct
d) None of these choices are correct
Collisions between which pairs of objects is likely to be nearly elastic? a) Two Baseballs b) A steel ball and a cotton ball c) A steel ball and a Baseball d) Two steel balls
d) Two steel balls
A person sits on a freely spinning lab stool that has no friction in its axle. When this person extends her arms a) her moment of inertia decreases and her angular speed increases b) her moment of inertia increases and her angular speed increases c) her moment of inertia increases and her angular speed remains the same d) her moment of inertia increases and her angular speed decreases e) her moment of inertia decreases and her angular speed decreases
d) her moment of inertia increases and her angular speed decreases
A rubber ball and a lump of clay have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The clay sticks to the wall. Which one of these objects experiences the great momentum change? a) the clay b) Both of them experience zero momentum change c) Both of them experience equal momentum change d) the ball
d) the ball
A merry-go-round spins freely when Diego moves quickly to the center along a radius of the merry-go-round. As he does this, it is true to say that. a) the moment of inertia of the system increases and the angular speed increases b) the moment of inertia of the system increases and the angular speed decreases c) the moment of inertia of the system decreases and the angular speed remains the same d) the moment of inertia of the system decreases and the angular speed increases e) the moment of inertia of the system decreases and the angular speed decreases
d) the moment of inertia of the system decreases and the angular speed increases
A 0.10kg ball traveling horizontally at 25 m/s, strikes a wall and rebounds at 19 m/s. What is the magnitude of the change in momentum of the ball during the rebound? a) 1.8 kg * m/s b) 1.2 kg * m/s c) 5.4 kg * m/s d) 72 kg * m/s e) 4.4 kg * m/s
e) 4.4 kg * m/s
A dinner plate falls vertically to the floor and breaks up into three pieces, which slide horizontally along the floor. Immediately after the impact, a 200g piece moves along the +x-axis with a speed of 2.00m/s, a 235g piece moves along the +y-axis with a speed of 1.50m/s. The third piece has a mass of 100g. What is the speed of the third piece? a) 2.51 m/s b) 2.57 m/s c) 6.83 m/s d) 3.50 m/s e) 5.33 m/s
e) 5.33 m/s
Although newton's second law, f = ma, is valid for collisions, it cannot generally be used in this form for collisions because a) the acceleration 'a' is too small b) the force F is not constant c) the acceleration 'a' occurs during a time interval too short to measure easily d) Both A and B e) Both B and C
e) Both B and C
A box is moved 10 m across a smooth floor by a force F making a downward angle with the floor so that there is effectively a 4N force acting parallel to the floor in the direction of motion and a 3 N force acting perpendicular to the floor. The force F acts for 20 seconds. The impulse delivered to the box by the floor during this process has magnitude. a) 80 Ns b) zero c) 100 Ns d) 60 Ns
e) Can't tell without knowing the weight of the box
The principle that total momentum does not change during a brief collision is a result of a) the definition of the kilogram b) the definition of the newton c) Newton's first law and Newton's second law d) Newton's first law and Newton's third law e) Newton's second law and Newton's third law
e) Newton's second law and Newton's third law
During a collision, which of these is an indication that the total momentum has changed? a) Sound is produced b) Deformation occurs c) Heat is generated d) All of these choices are indication that the kinetic energy has changed e) None of these choices are correct
e) None of these choices are correct
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? a) Hitting the brick wall b) We cannot answer this question without more information c) HItting the other car d) None of these is true e) The force would be the same in both cases
e) The force would be the same in both cases
A small car meshes with a large truck in a head-on collision. Which of the following statements concerning the magnitude of the average force during the collision is correct? a) The truck experiences the greater average force b) the small car experiences the greater average force c) The force experienced by each one is inversely proportional to its mass d) The fore experienced by each one is directly proportional to its mass e) The small car and the truck experience the same average force
e) The small car and the truck experience the same average force
A railroad car collides with and sticks to an identical railroad car that is initially at rest. After the collision, the kinetic energy of the system a) is one fourth as much as before b) is one quarter as much as before c) is the same as before d) is one third as much as before e) is half as much as before
e) is half as much as before
Two astronauts of equal mass are holding on to eachother and moving at a speed of 30 m/s They push off each other and one of the astronauts moves in the same direction as the two were initially moving but at 60 m/s The velocity of the second astronaut is a) 30 m/s backward b) 30 m/s forward c) 60 m/s backward d) 60 m/s forward e) zero
e) zero
A 328 kg car moving at 19.1 m/s hits from behind another car moving at 13.0 m/s in the same direction. If the second car has a mass of 790 kg and a new speed of 15.1 m/s, what is the velocity of the first car after the collision? a) 14.0 m/s b) 18.2 m/s c) 24.2 m/s d) -14.0 m/s
mV + Mv = mU + Mu we solve for U = (mV + Mv - Mu)/m = (328*19.1 + 790*13 - 790*15.1)/328 = 14 a) 14.0 m/s
