Energy

1
Energy
2
A crane lowers a steel girder into place at a
construction site. The girder moves with constant
speed. Consider the work Wg done by gravity and
the work WT done by the tension in the cable.
Which of the following is correct?

1. Wg is positive and WT is positive.
2. Wg is negative and WT is negative.
3. Wg is positive and WT is negative.
4. Wg and WT are both zero.
5. Wg is negative and WT is positive.

3
A crane lowers a steel girder into place at a
construction site. The girder moves with constant
speed. Consider the work Wg done by gravity and
the work WT done by the tension in the cable.
Which of the following is correct?

1. Wg is positive and WT is positive.
2. Wg is negative and WT is negative.
3. Wg is positive and WT is negative.
4. Wg and WT are both zero.
5. Wg is negative and WT is positive.

The tension force is opposite the direction of
motion while the gravitational force is in the
same direction as the motion. The cos(theta) term
in the work formula is negative.
4
Which force does the most work?

1. The 6 N force.
2. The 8 N force.
3. The 10 N force.
4. They all do the same amount of work.

5
Which force does the most work?

1. The 6 N force.
2. The 8 N force.
3. The 10 N force.
4. They all do the same amount of work.

6
Rank in order, from largest to smallest, the
gravitational potential energies of balls 1 to 4.

1. (Ug)1 gt (Ug)2 gt (Ug)3 gt (Ug)4
2. (Ug)4 gt (Ug)3 gt (Ug)2 gt (Ug)1
3. (Ug)1 gt (Ug)2 (Ug)4 gt (Ug)3
4. (Ug)3 gt (Ug)2 (Ug)4 gt (Ug)1
5. (Ug)4 (Ug)2 gt (Ug)3 gt (Ug)1

7
Rank in order, from largest to smallest, the
gravitational potential energies of balls 1 to 4.

1. (Ug)1 gt (Ug)2 gt (Ug)3 gt (Ug)4
2. (Ug)4 gt (Ug)3 gt (Ug)2 gt (Ug)1
3. (Ug)1 gt (Ug)2 (Ug)4 gt (Ug)3
4. (Ug)3 gt (Ug)2 (Ug)4 gt (Ug)1
5. (Ug)4 (Ug)2 gt (Ug)3 gt (Ug)1

Use the formula U mgy
8
A small child slides down the four frictionless
slides AD. Each has the same height. Rank in
order, from largest to smallest, her speeds vA to
vD at the bottom.

1. vA vB vC vD
2. vD gt vA vB gt vC
3. vD gt vA gt vB gt vC
4. vC gt vA vB gt vD
5. vC gt vB gt vA gt vD

9
A small child slides down the four frictionless
slides AD. Each has the same height. Rank in
order, from largest to smallest, her speeds vA to
vD at the bottom.

1. vA vB vC vD
2. vD gt vA vB gt vC
3. vD gt vA gt vB gt vC
4. vC gt vA vB gt vD
5. vC gt vB gt vA gt vD

10
A spring-loaded gun shoots a plastic ball with a
speed of 4 m/s. If the spring is compressed twice
as far, the balls speed will be

1. 16 m/s.
2. 8 m/s.
3. 4 m/s.
4. 2 m/s.
5. 1 m/s.

11
A spring-loaded gun shoots a plastic ball with a
speed of 4 m/s. If the spring is compressed twice
as far, the balls speed will be

1. 16 m/s.
2. 8 m/s.
3. 4 m/s.
4. 2 m/s.
5. 1 m/s.

12
Four students run up the stairs in the time
shown. Rank in order, from largest to smallest,
their power outputs Pa to Pd.

1. Pb gt Pa Pc gt Pd
2. Pd gt Pa Pb gt Pc
3. Pd gt Pb gt Pa gt Pc
4. Pb gt Pa gt Pc gt Pd
5. Pc gt Pb Pa gt Pd

13
Four students run up the stairs in the time
shown. Rank in order, from largest to smallest,
their power outputs Pa to Pd.

1. Pb gt Pa Pc gt Pd
2. Pd gt Pa Pb gt Pc
3. Pd gt Pb gt Pa gt Pc
4. Pb gt Pa gt Pc gt Pd
5. Pc gt Pb Pa gt Pd