Ch 7 Homework.

10 N.

About 40 J is required to push a crate 4 m across a floor. If the push is in the same direction as the motion of the crate, the force on the crate is about

The skater's potential energy is at its maximum value at the locations where the skater turns and goes back in the opposite direction.

As the skater is skating back and forth, where does the skater have the most potential energy?

The kinetic energy at the bottom of the ramp is equal to the amount of potential energy loss in going from the initial location to the bottom.

Based on the previous question, which statement is true?

It decreases...

How does the force needed to turn the wrench change if you increase the lever arm?

It decreases

How does the lever arm change if you decrease the angle of the force?

It decreases.

How does the lever arm change when you decrease the distance to the nut?

It decreases..

How does the lever arm change when you decrease the distance to the nut?

2205 J

If the skater started from rest 4 m above the ground (instead of 7m), what would be the kinetic energy at the bottom of the ramp (which is still 1 m above the ground)?

1 3 5,2 4

If the skater starts from rest at position 1, rank, in increasing order from least to greatest, the kinetic energy of the skater at the five positions shown. Rank from smallest to largest. To rank items as equivalent, overlap them.

11 m/s

One common application of conservation of energy in mechanics is to determine the speed of an object. Although the simulation doesn't give the skater's speed, you can calculate it because the skater's kinetic energy is known at any location on the track. Consider again the case where the skater starts 7 m above the ground and skates down the track. What is the skater's speed when the skater is at the bottom of the track?

D B C E A

Rank KE from greatest to least at each point. Rank from greatest to least. To rank items as equivalent, overlap them.

A E C B D

Rank PE from greatest to least at each point. Rank from greatest to least. To rank items as equivalent, overlap them.

D B C E A

Rank speed from greatest to least at each point. Rank from greatest to least. To rank items as equivalent, overlap them.

bottom of its swing.

The bob of a simple pendulum has its maximum kinetic energy at the

KE = 1.0×104 J

What is his kinetic energy when his potential energy reduces to 1000 J? Express your answer to two significant figures and include the appropriate units.

the same.

When one does twice the work in twice the time, the power expended is _______.

The speed is higher, but less than twice as fast.

When the skater starts 7 m above the ground, how does the speed of the skater at the bottom of the track compare to the speed of the skater at the bottom when the skater starts 4 m above the ground?

by four.

When traveling twice as fast your kinetic energy is increased _______.

The skater's kinetic energy is at its maximum value at the lowest point of the track.

Where on the track is the skater's kinetic energy the greatest?

four times as much.

he work that is done when twice the load is lifted twice the distance is _______.

2 m.

A 2-kg box of taffy candy has 40 J of potential energy relative to the ground. Its height above the ground is

all of the above

A circus diver drops from a high pole into water far below. When he is halfway down

destroyed.

Energy cannot be _______.

1. total energy at initial position= 5145 J 2. potential energy at initial position= 5145 J 3. kinetic energy at initial position= 0 J 4. total energy at the bottom of track= 5145 J 5. potential energy at bottom of track= 735 J 6. kinetic energy at the bottom of track= 4410 J

Match the approximate numerical values on the left with the energy type categories on the right to complete the equations. Assume that the mass of the skater is 75.0 kg and that the acceleration of gravity is 9.8 N/kg .

The total energy is the same at all locations of the track.

Observe the total energy bar on the Bar Graph. As the skater is skating back and forth, which statement best describes the total energy?

four times the kinetic energy.

Two identical golf carts move at different speeds. The faster cart has twice the speed and therefore has