Chapter 7

Three masses, 1.0 kg, 2.0 kg, and 3.0 kg, are located at (0.0m, 0.0m), (1.0m,1.0m), and (2.0m,-2.0m) respectively. What is the location of the center of mass of this system?

(1.3m, -0.67m)

A 1.0-kg bead is at (-2.0 cm, 2.0 cm), a 2.0-g bead is at (2.0 cm, -4.0 cm), and a 3.0-g bead is at (2.0cm, 0.0cm). What are the coordinates of the center of mass of this system of beads?

1.3 cm, -1.0 cm

The momentum of an isolated system is conserved A) in both elastic and inelastic collisions B) only in elastic collisions C) only in inelastic collisions

A) 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 upward. Which of the following statements about the bounce are correct? A) The magnitude of the ball's momentum was the same just before and just after the bounce B) The ball's momentum was conserved during the bounce. C) The ball had the same momentum just before and just after the bounce. D) None of the above statements are correct

A) The magnitude of the ball's momentum was the same just before and just after the bounce

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 half 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 one fourth as much before

A) is half as much as before

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) stationary B) moving backward C) moving forward

A) stationary

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 which it hit. The clay sticks to the wall. Which one of these objects experience the greater momentum change? A) the ball B) the clay C) Both of them experience the same momentum change D) Both of them experience zero momentum change.

A) the ball

In a 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) elastic C) completely inelastic

B) elastic

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? 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

A tiger is running in a straight line. If we double both the mass and the speed of the tiger, the magnitude of its momentum will increase by what factor? A) 2 B) 4 C) 16 D) 8

B)4

A fire hose is turned on the door of a burning building in order to knock the door down. This requires a force of 1000 N. If the hose delivers 40 kg of water per second, what is the minimum velocity of the stream needed to knock the down the door, assuming the water doesn't bounce back? A) 30 m/s B) 20 m/s C) 15 m/s D) 25 m/s

D) 25 m/s

A steady horizontal force lasting for 2.1s gives a 1.25 kg object an acceleration of 3.2 m/s^2 on a frictionless table. What impulse does this force give to the object? A) 26 kg*m/s B) 11 kg*m/s C) 2.6 kg*m/s D) 8.4 kg*m/s

D) 8.4 kg*m/s

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) 1/4 as great as the momentum change of the heavier fragment C) 5 times as great as the momentum change of the heavier fragment D) The same as the momentum change of the heavier fragment E) 1/25 as great as the momentum change of the heavier fragment

D) The same as the momentum change of the heavier fragment

A small 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 experiences the greater magnitude momentum change. B) The magnitude of the momentum change experienced by each one is directly proportional to its mass C) The magnitude of the momentum change experienced by each one is inversely proportional to mass D) The small car and the truck experience the same magnitude momentum change E) The truck experiences the greater magnitude momentum change

D) The small car and the truck experience the same magnitude momentum change

If a quantity you calculated had units of kg * m/s, what type of quantity could it be? A) impulse B) force C) work D) momentum E) kinetic energy

D) momentum

Two air track carts move along an air track towards each other. Cart A has a mass of 450 g and moves toward the right with a speed of 0.850 m/s. Cart B has a mass of 300 g and moves toward the left with a speed of 1.12 m/s. What is the total momentum of the two-cart system? A) 0.719 to the right B) 0.750 to the left C) 0.750 to the right D) 0.719 to the left E) 0.047 to the right

E) 0.047 to the right

A 0.140-kg baseball is dropped from rest. It has a speed of 1.20 m/s just before it hits the ground, and it rebounds with an upward speed of 1.00 m/s. The ball is in contact with the ground for 0.0140 s. What is the average force exerted by the ground on the ball during the time of contact? A) 22.0 N downwards B) 2.00 N upwards C) 0.00 N D) 2.00 N downwards E) 22.0 N upwards

E) 22.0 N upwards Velocity going down is negative

Which of the following quantities are units of momentum? A) N * m B) kg * m C) kg * s/m D) N * s E) kg * m/s

E) kg * m/s