Chapter 7 concepts

Which of the following statements is/are true?

A person's power output limits the amount of work that he or she can do in a given time span Power is the rate at which energy is transformed. Power is the rate at which work is done. The SI unit of power is the watt.

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

Negative -When an object's displacement has a component in a direction opposite that of a given force, that force does negative work on the object

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. E = P * T 2E = n*P * T/2 n = 4 B's power output is four times A's. Power = work / time so P2/P1 = W2/ W1 * T1/ T2 [ W2/W1 = 2 as the work is twice as great. T2/T1 = 1/2 as it is half the time so T1/T2 = 2 ] = 2 * 2 = 4

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.

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 -When the net work done on an object is zero, there is no overall change in the object's kinetic energy

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

The same magnitude and sign -The kinetic energy of a moving object is always positive, regardless of the direction it is moving in, or the coordinate system used

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. Because from the formula of work: W = Fd since there are no displacement with respect by the gravity (y a-xis/ downward) since the object only moves horizontally and not sliding/falling. W = 20 ( 0 meters downward) = 0 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. work is the product of the component of force in the direction of motion x displacement while the ball is going up, the direction of motion and the direction of the force of gravity are opposite, so the work is negative, another way to realize this is that the force (gravity) is slowing the ball down while the ball is descending, the force and direction of motion are in the same direction (the ball's speed increases) and the work done is positive