1. Q6.1
A weight lifter lifts a barbell upward from the floor. While he is lifting it,
1. he does positive work on the barbell and the barbell does positive work on him
2. he does positive work on the barbell and the barbell does negative work on him
3. he does negative work on the barbell and the barbell does positive work on him
4. he does negative work on the barbell and the barbell does negative work on him

2. A6.1
A weight lifter lifts a barbell upward from the floor. While he is lifting it,
1. he does positive work on the barbell and the barbell does positive work on him
2. he does positive work on the barbell and the barbell does negative work on him
3. he does negative work on the barbell and the barbell does positive work on him
4. he does negative work on the barbell and the barbell does negative work on him

3. Q6.2
A weight lifter lowers a barbell to the floor. While he is lowering it,
1. he does positive work on the barbell and the barbell does positive work on him
2. he does positive work on the barbell and the barbell does negative work on him
3. he does negative work on the barbell and the barbell does positive work on him
4. he does negative work on the barbell and the barbell does negative work on him

4. A6.2
A weight lifter lowers a barbell to the floor. While he is lowering it,
1. he does positive work on the barbell and the barbell does positive work on him
2. he does positive work on the barbell and the barbell does negative work on him
3. he does negative work on the barbell and the barbell does positive work on him
4. he does negative work on the barbell and the barbell does negative work on him

5. Q6.3
Two iceboats (one of mass m, one of mass 2m) hold a race on a frictionless, horizontal, frozen lake. Both iceboats start at rest, and the wind exerts the same constant force on both iceboats.
Which iceboat crosses the finish line with more kinetic energy (KE)?
1. the iceboat of mass m: it has twice as much KE as the other
2. the iceboat of mass m: it has 4 times as much KE as the other
3. the iceboat of mass 2m: it has twice as much KE as the other
4. the iceboat of mass 2m: it has 4 times as much KE as the other
5. they both cross the finish line with the same kinetic energy

6. A6.3
Two iceboats (one of mass m, one of mass 2m) hold a race on a frictionless, horizontal, frozen lake. Both iceboats start at rest, and the wind exerts the same constant force on both iceboats.
Which iceboat crosses the finish line with more kinetic energy (KE)?
1. the iceboat of mass m: it has twice as much KE as the other
2. the iceboat of mass m: it has 4 times as much KE as the other
3. the iceboat of mass 2m: it has twice as much KE as the other
4. the iceboat of mass 2m: it has 4 times as much KE as the other
5. they both cross the finish line with the same kinetic energy

7. Q6.4
A tractor driving at constant speed pulls a sled loaded with firewood. There is friction between the sled and the road.
After the sled has moved a distance d, the total work done on the sled is
1. positive
2. negative
3. zero
4. not enough information given to decide

8. A6.4
A tractor driving at constant speed pulls a sled loaded with firewood. There is friction between the sled and the road.
After the sled has moved a distance d, the total work done on the sled is
1. positive
2. negative
3. zero
4. not enough information given to decide

9. Q6.5
A nonzero net force acts on an object. Which of the following quantities could be constant?
1. the object’s kinetic energy
2. the object’s speed
3. the object’s velocity
4. both 1. and 2.
5. all of 1., 2., and 3.

10. A6.5
A nonzero net force acts on an object. Which of the following quantities could be constant?
1. the object’s kinetic energy
2. the object’s speed
3. the object’s velocity
4. both 1. and 2.
5. all of 1., 2., and 3.

11. Q6.6
An object is initially at rest. A net force (which always points in the same direction) is applied to the object so that the power of the net force is constant. As the object gains speed,
1. the magnitude of the net force remains constant
2. the magnitude of the net force increases
3. the magnitude of the net force decreases
4. not enough information given to decide

12. A6.6
An object is initially at rest. A net force (which always points in the same direction) is applied to the object so that the power of the net force is constant. As the object gains speed,
1. the magnitude of the net force remains constant
2. the magnitude of the net force increases
3. the magnitude of the net force decreases
4. not enough information given to decide