Chapter 7 Physics Test Review
A 6.0 × 10⁻² kg tennis ball moves at a speed of 12 m/s. The ball is struck by a racket, causing it to rebound in the opposite direction at a speed of 18 m/s. What is the change in the ball's momentum?
-1.8 kg•m/s ∆p = m(∆V) = (6.0 × 10⁻²)(-18-12) = -1.8 kg•m/s
A swimmer with a mass of 75 kg dives off a raft with a mass of 500 kg. If the swimmer's speed is 4 m/s immediately after leaving the raft, what is the speed of the raft?
0.6 m/s (75)(0) + (500)(0) = (75)(4) + (500)(v) = 0.6 m/s
A 90 kg halfback runs north and is tackled by a 120 kg opponent running south at 4 m/s. The collision is perfectly inelastic. Just after the tackle, both players move at a velocity of 2 m/s north. Calculate the velocity of the 90 kg player just before the tackle.
10 m/s to the north (90)(v) + (120)(-4) = (90 + 120)(2) = 10 m/s to the north
A baseball bat strikes a baseball with a force of 35 N. The bat is in contact with the ball for 0.12 s. What is the magnitude of the change in momentum of the ball?
4.2 kg•m/s ∆p = F(∆T) = (35)(0.12) = 4.2 kg•m/s
A bowling ball with a mass of 7.0 kg strikes a pin that has a mass of 2.0 kg. The pin flies forward with a velocity of 6.0 m/s, and the ball continues forward at 4.0 m/s. What was the original velocity of the ball?
5.7 m/s forward (7)(v) + (2)(0) = (7)(4) + (2)(6) = 5.7 m/s forward
A ball with a momentum of 4.0 kg•m/s hits a wall and bounces straight back without losing any kinetic energy. What is the change in the ball's momentum? a. -8.0 kg•m/s b. -4.0 kg•m/s c. 0.0 kg•m/s d. 8.0 kg•m/s
A
In a two-body collision, a. momentum is always conserved. b. kinetic energy is always conserved. c. neither momentum nor kinetic energy is conserved. d. both momentum and kinetic energy are always conserved.
A
Two objects move separately after colliding, and both the total momentum and total kinetic energy remain constant. Identify the type of collision. a. elastic b. nearly elastic c. inelastic d. perfectly inelastic
A
Two objects with different masses collide and bounce back after an elastic collision. Before the collision, the two objects were moving at velocities equal in magnitude but opposite in direction. After the collision, a. the less massive object had gained momentum. b. the more massive object had gained momentum. c. both objects had the same momentum. d. both objects lost momentum.
A
Which of the following situations is an example of a significant change in momentum? a. A tennis ball is hit into a net. b. A helium-filled balloon rises upward into the sky. c. An airplane flies into some scattered white clouds. d. A bicyclist rides over a leaf on the pavement.
A
How can a small force produce a large change in momentum?
A small force can produce a large change in momentum if the force acts on an object for a long period of time.
A 75 kg person walking around a corner bumped into an 80 kg person who was running around the same corner. The momentum of the 80 kg person a. increased. b. decreased. c. remained the same. d. was conserved.
B
A roller coaster climbs up a hill at 4 m/s and then zips down the hill at 30 m/s. The momentum of the roller coaster a. is greater up the hill than down the hill. b. is greater down the hill than up the hill. c. remains the same throughout the ride. d. is zero throughout the ride.
B
The change in an object's momentum is equal to a. the product of the mass of the object and the time interval. b. the product of the force applied to the object and the time interval. c. the time interval divided by the net external force. d. the net external force divided by the time interval.
B
Two swimmers relax close together on air mattresses in a pool. One swimmer's mass is 48 kg, and the other's mass is 55 kg. If the swimmers push away from each other, a. their total momentum triples. b. their momenta are equal but opposite. c. their total momentum doubles. d. their total momentum decreases.
B
Which of the following is most closely related to mass? a. inertia in motion b. inertia c. momentum d. change in momentum
B
Which of the following statements about the conservation of momentum is not correct? a. Momentum is conserved for a system of objects pushing away from each other. b. Momentum is not conserved for a system of objects in a head-on collision. c. Momentum is conserved when two or more interacting objects push away from each other. d. The total momentum of a system of interacting objects remains constant regardless of forces between the objects.
B
A billiard ball with a stationary identical billiard ball in an elastic head-on collision. After the collision, which is true of the first ball? a. It maintains its initial velocity. b. It has one-half its initial velocity. c. It comes to rest. d. It moves in the opposite direction.
C
A rubber ball moving at a speed of 5 m/s hit a flat wall and returned to the thrower at 5 m/s. The magnitude of the momentum of the rubber ball a. increased. b. decreased. c. remained the same. d. was not conserved.
C
If a force is exerted on an object, which statement is true? a. A large force always produces a large change in the object's momentum. b. A large force produces a large change in the object's momentum only if the force is applied over a very short time interval. c. A small force applied over a long time interval can produce a large change in the object's momentum. d. A small force always produces a large change in the object's momentum.
C
The impulse experienced by a body is equivalent to the body's change in a. velocity. b. kinetic energy. c. momentum. d. force.
C
When comparing the momentum of two moving objects, which of the following is correct? a. The object with the higher velocity will have less momentum if the masses are equal. b. The more massive object will have less momentum if its velocity is greater. c. The less massive object will have less momentum if the velocities are the same. d. The more massive object will have less momentum if the velocities are the same.
C
In an inelastic collision between two objects with unequal masses, a. the total momentum of the system will increase. b. the total momentum of the system will decrease. c. the kinetic energy of one object will increase by the amount that the kinetic energy of the other object decreases. d. the momentum of one object will increase by the amount that the momentum of the other object decreases.
D
Two objects stick together and move with a common velocity after colliding. Identify the type of collision. a. elastic b. nearly elastic c. inelastic d. perfectly inelastic
D
A 1.0-kg ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. What is the change in momentum of the ball? a. zero kg • m/s b. 12 kg • m/s, downward c. 12kg • m/s, upward d. 24 kg • m/s, downward e. 24 kg • m/s, upward
E
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 provides the necessary force to stop the person. b. The bag reduces the impulse to the person. c. The bag increases the amount of time the force acts on the person and reduces the change in momentum. d. The bag decreases the amount of time during which the momentum is changing and reduces the average force on the person. e. The bag increases the amount of time during which the momentum is changing and reduces the average force on the person.
E
Which one of the following is true concerning momentum? a. Momentum is a force. b. Momentum is a scalar quantity. c. The SI unit of momentum is kg • m2/s. d. The momentum of an object is always positive. e. Momentum and impulse are measured in the same units.
E
Distinguish between impact and impulse. Which designates a force and which is the force multiplied by time?
Impact is a force; impulse is the force multiplied by time.
Distinguish between an elastic and an inelastic collision.
No kinetic energy is lost during an elastic collision. Objects are distorted and generate heat during an inelastic collision.
As a bullet travels through the air, it slows down due to air resistance. How does the bullet's momentum change as a result?
The bullet's momentum decreases as its speed decreases.
In terms of momentum conservation, why does a cannon recoil when fired?
The cannon's momentum must be equal and opposite to the cannonball.
Which has a greater momentum—a truck with a mass of 2250 kg moving at a speed of 25 m/s or a car with a mass of 1210 kg moving at a speed of 51 m/s?
The car has a greater momentum. car: p= (2250)(25)= 56,250 truck: p= (1210)(51)= 61,710
A baseball pitcher's first pitch is a fastball, moving at high speed. The pitcher's second pitch—with the same ball—is a changeup, moving more slowly. Which pitch is harder for the catcher to stop? Explain your answer in terms of momentum.
The first pitch is harder to stop. The first pitch has greater momentum because it has a greater velocity, so the change in momentum to zero is greater.
State, in words, the law of conservation of momentum for an isolated system.
The total momentum of all objects interacting with one another remains constant regardless of the nature of the forces between the objects.
Why is it advantageous for a boxer to ride with the punch? Why should he avoid moving into an oncoming punch?
When the boxer rides with the punch, the time of impact is extended and the force is reduced. Moving into the punch would shorten the time and increase the force.
For a constant force, suppose the duration of impact on an object is doubled. How much is the impulse increased? -- How much is the resulting change in momentum increased?
doubled -- doubled
How do you convert g to kg?
grams/1,000 (example: 25g = 0.025kg)
Name that term. -- change in momentum
impulse
Name that term. -- inertia in motion
momentum
Which has a greater momentum: a heavy truck at rest or a moving skateboard? -- Which has greater mass?
moving skateboard (greater momentum) -- truck (greater mass)
What is the formula of momentum?
p=mv
Visualize yourself on a skateboard. When you throw a ball, do you experience an impulse? -- Do you experience an impulse when you catch a ball of the same speed? -- Do you experience an impulse when you catch it and then throw it out again? -- Which impulse is greatest?
yes -- yes -- yes -- The impulse is greatest when catching then throwing.
