Physics Ch. 6&7

A wooden box is pulled horizontally on a rough carpet, and as a result it is moving with constant velocity through a distance d. Considering the box as the system, which of the following expressions shows the work done by external forces on the box?

( fpull - fk carpet on box)x d

A person exerts a 50-N pushing force on a friend rolling up an 8° steep hill on rollerblades. The force is parallel to the hill and is exerted the whole time that the friend rolls a distance of 100 m up the hill. Which of the following expressions is correct for the work done by this pushing force on the friend?

(50)(100)cos(0) J

Which of the following statements are true? Select all correct responses.

-The vector sum of forces exerted on a particle equals the rate of change of momentum of the particle with respect to time. -The total momentum of any number of particles is equal to the vector sum of the momenta of the individual particles. -The total momentum of an isolated system is constant.

You load an arrow into a bow and pull the bowstring back 0.50 m. The bow has a spring constantk = 2000 N/m. What is the potential energy of the bowstring?

250 J

Object A of unknown mass and speed is moving east and has a collision with object B of different unknown mass and speed moving south. If they were to stick together after the collision, in which direction will they be moving?

Between east and south

When a bow string is stretched all the way back and held in this position, it has the following type of energy.

Elastic Potential

Energy is a conserved quantity, meaning that...

If no work is done on the system, the energy of the system will not change.

A ball rolls at constant speed on a horizontal table toward a semicircular barrier as shown in the figure. When it is in contact with the barrier, what can we conclude about the net force on the ball?

It is perpendicularto the motion of the ball.

In an inelastic collision of two objects, which of the following quantities is constant for the system of these two objects?

Momentum

A lump of putty and a rubber ball have equal mass. Both are thrown with equal speed against a wall. The putty sticks to the wall. The ball bounces back at nearly the same speed with which it hit the wall. Which object has the greater momentum change?

The ball has the greater momentum change.

Which one of these objects has the greater magnitude of linear momentum? A baseball of mass 150 grams moving at 40 m/s or a soccer ball of mass 500 grams moving at 12 m/s

The baseball and the soccer ball have the same momentum.

Compare the gravitational force Earth exerts on an apple with the gravitational force an apple exerts on Earth.

The force the apple exerts on Earth is the same magnitude as the force Earth exerts on the apple.

What represents the impulse of the force in a graph of force versus time?

The impulse is equal to the area under the curve.

In a lab environment, you are investigating the impulse of a force exerted on a brick when the brick's speed is reduced from 2.5 m/s to a complete stop. First, you allow the brick to slam into a secured piece of wood, bringing the brick to a sudden stop. Second, you allow the brick to plow into a large slab of gelatin so that the brick comes to a gradual halt. In which situation is there a greater impulse of the force on the brick?

The impulse is the same in both situations.

Two identical balls are thrown vertically upward. The second ball is thrown with an initial speed that is twice that of the first ball. How does the maximum height of the two balls compare?

The maximum height of the second ball is four times that of the first ball.

A compact car and a large truck collide head-on and stick together. Which undergoes the larger momentum change?

The momentum change is the same for both vehicles

Which statement must be true for the momentum of a system to be conserved?

The net external force on the system is zero.

While goofing off at the ice skating rink, a student takes off her shoes and places each of them on the ice. Her friend, a hockey player, then shoots a hockey puck at each shoe. The first puck immediately comes to rest after it collides with the left shoe. The second puck rebounds after it collides with the right shoe. If each hockey puck has the same incoming speed, which shoe has greater speed after the collision?

The right shoe

An object's change in momentum during a time interval depends on

The total external forces acting on the object, the length of the time interval

Two objects are moving at equal speed along a level, frictionless surface. The second object has twice the mass of the first object. They both slide up the same frictionless incline plane. Which object rises to a greater height? Choose the answer with the best explanation.

The two objects rise to the same height.

For the linear impulse and momentum equations for the particle system, which of the following impulsive forces can be included?

external force explosive force friction force

A motorcycle drives up a steeply inclined ramp. The work done on the motorcycle by the Earth's gravitational force is ____.

negative

During a certain time interval, the net work done on an object is zero joules. We can be certain that ____

the object's final speed was the same as its initial speed

A person exerts a horizontal 50 N force on a crate, causing it to move horizontally at a constant speed through a distance of 10 m. What is the work done by the person on the crate?

The work done on the crate is 500 J.

An object (the system) weighing 20 N moves horizontally toward the right a distance of 5.0 m. What is the work done on the object by the gravitational force?

The work done on the object by the gravitational force is zero joules.

Identify which one of these systems can be considered as constituting an isolated system.

Two pucks colliding on a frictionless ice surface. The two pucks are the system and the ice surface is external to the system.

A ball (the system) is thrown straight upward. How does the sign of the work done by the gravitational force while the ball is traveling upward compare with the sign of the work done by the gravitational force while the ball is traveling downward?

Work done by the gravitational force is negative while the ball is traveling upward and positive while the ball is traveling downward.