Momentum
1. What does the equation p = mv mean? Write a one-sentence answer.
2. What is the momentum of a 60 kg sprinter running at 8.0 m/s?
3. What is the same sprinter’s velocity if she has a momentum of 400 kg m/s?
4. If the same sprinter had half the momentum, how would her velocity change?
5. A falling boulder hits the ground at a velocity of 15 m/s, losing 1,200 kg m/s of momentum to the
Earth when it stops. What is its mass?
6. A 4,000 kg truck and a 2,000 kg car are both traveling at 10 m/s when they hit a wall. Which
vehicle has more momentum just before striking the wall? What is the ratio of their momenta?
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7. Which of these objects has the greatest momentum? Which has the least momentum?
A.
B.
C.
D.
a 6.0 kg bowling ball moving at 8.0 m/s
a 3.0 gram pellet fired at 250 m/s
a 2500 kg truck parked on a side street
a 60 kg student walking at 1.0 m/s
8. Derive an equation that shows how the momentum of a falling object changes over time. Assume
that there is no friction and that the object starts with zero initial velocity.
9. When one object loses momentum, another object gains momentum. This exchange of momentum
is closely related to Newton’s laws. To prove this, do the following algebraic calculation.
a. Newton’s second law can be written: F = ma.
Starting from this form, substitute a = (vf - vi)/Δt .
b. Rewrite the equation in terms of the
initial and final momentum, pi and pf.
c. This new equation says “the change in momentum = something.” What is the “something”?
What physical quantity does this “something” represent?
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