Chapter 7, Part 2

October 21, 2005

Two boxes, one heavier than the other, are initially at rest on a horizontal frictionless surface. The same

constant force F acts on each one for exactly 1 second. Which box has more momentum after the force acts?

60

1 2 3 4 5

F F light heavy

33%

33%

33% 1. The lighter one.

2. The heavier one.

3. Both the same.

For the same situation as the previous problem, which box has the larger velocity after the force acts?

60

1 2 3 4 5

F F light heavy

33%

33%

33% 1. The lighter one.

2. The heavier one.

3. Both the same.

Consider the following “Geophysical weapon”: what would Consider the following “Geophysical weapon”: what would happen if the entire country of China jumped at once?happen if the entire country of China jumped at once?

60

1 2 3 4 5

33%

33%

33%1. The earth’s orbit would be measurably

perturbed.2. Nothing since the resulting momentum of

the earth would be so much less than the momentum of the people

3. Nothing since the resulting velocity of the earth would be so much less than the velocity of the people

A racquet ball is placed on top of a basketball and both are A racquet ball is placed on top of a basketball and both are dropped from height dropped from height hh above the ground. The two balls above the ground. The two balls collide as the basketball recoils from the ground. The collide as the basketball recoils from the ground. The

resulting height of the racquet ball after the collision isresulting height of the racquet ball after the collision is 60

1 2 3 4 5

33%

33%

33% 1. Equal to h.

2. Less than h.

3. Greater than h.

Just as basketball recoils

Answers

1. 3 – both the same, see above

2. 1 – the lighter one, p=mv, if same p then small m means big v

3. 3 – p is same for both, but Mearth is huge, so tiny v

4. 3 - greater than, little guy gets a boost from the big guy (basis of supernova explosions, gravitationally inward falling outer material crashes into outward exploding inner material creating tremendous velocities – populates the universe with the various elements)