Physics 1 Chapter 7 Concepts

Which of the following statements is/are true?

- A potential energy function can be specified for a conservative force. - A conservative force permits a two-way conversion between kinetic and potential energies. - The work done by a nonconservative force depends on the path taken.

Which of the following statements is/are true?

- The SI unit of power is the watt. - A person is limited in the total work he or she can do during a limited period of time by the rate at which energy can be transformed. - Power is the rate at which energy is transformed. - Power is the rate at which work is done.

Which of the following statements is/are true?

- The total mechanical energy of a system is constant only if conservative forces act. - Mechanical energy can be dissipated to nonmechanical forms of energy.

Part B You are riding on a roller coaster that starts from rest at a height of 25.0 m and moves along a frictionless track. How fast are you moving when you reach the top of the loop, at point B?

16.0 m/s

Part A You are riding on a roller coaster that starts from rest at a height of 25.0 m and moves down a frictionless track to a height of 3.00 m. How fast are you moving when you arrive at the 3.00-m height?

20.8 m/s

Part C You are riding on a roller coaster that starts from rest at a height of 25.0 m and moves along a frictionless track. However, after a bad storm some leaves settled on part of the track causing a 9.4-m length of the track to exert a frictional force of 625 N on the car. To safely make it around the loop, the 50-kg car must have a minimum speed of 7.7 m/s at the top of the loop (point B). How fast should the car be moving initially at point A to ensure that it reaches the top of the loop with the minimum required speed?

6.28 m/s

Part D The amount of kinetic energy an object has depends on its mass and its speed. Rank the following sets of oranges and cantaloupes from least kinetic energy to greatest kinetic energy. If two sets have the same amount of kinetic energy, place one on top of the other.

Least to Greatest Least- cantaloupe w/ mass 4m speed 1/4v 2 oranges w/ mass 2m speed 1/2v 1 orange w/ mass m speed v Greatest- (2) 1 cantaloupe w/ mass 4m speed v 4 oranges w/ mass 4m speed v

Person B does twice the work of person A, and in one-half of the time . How does the power output of person B compare to person A?

Person B has four times the power output of person A.

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

The net work done on the crate is zero joules.

If the net work done on an object is positive, what can you conclude about the object's motion? Assume the object is in the absence of any other forces or friction.

The object is speeding up.

If the net work done on an object is zero, what can you determine about the object's kinetic energy?

The object's kinetic energy remains the same.

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?

The two objects rise to the same height.

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

negative

Part C 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

Part A Two identical cars are driving in opposite directions at the same speed. Their kinetic energies have ____.

the same magnitude and sign

A graph depicts force versus position. What represents the work done by the force over the given displacement?

The work done is equal to the area under the curve.

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

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

A ball is thrown straight upward. How does the sign of the work done by gravity while the ball is traveling upward compare with the sign of the work done by gravity while the ball is traveling downward?

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