Download Momentum - GregoriusMomentumLesson

Momentum Review Questions
Physics
Study Guide
Momentum
Know the definition of momentum (mass x velocity)
Be able to calculate momentum, mass or velocity given the other two
Be able to explain which of two objects will have more momentum and why
Impulse and Change in Momentum
Know what an impulse is (force exerted x time the force acts)
Know that the impulse on an object is equal to the change in the object's momentum
Be able to find the change in momentum given initial momentum and final momentum
Be able to calculate change in momentum/impulse, force or time given the other two
Be able to explain how to increase the impulse on an object (and therefore change its momentum by a greater amount)
Be able to give and explain situations where you would want a large impulse and how you would get it
Know that for a given impulse (a fixed change in momentum) there are many combinations of force and time that work
Know that for a given impulse, the force and the time that the force acts are inversely related
Be able to explain the different effects of a quick change in momentum versus a more gradual change in momentum for
several different situations
Conservation of Momentum
Know that when two objects collide or interact, the impulse on one object is equal and opposite to the impulse on the other
Know that any momentum lost by one object in a collision or interaction is gained by the other object
Be able to state the law of conservation of momentum: If there are no outside forces acting on a system, the momentum of
the system remains the same.
Be able to explain how the law of conservation of momentum applies to simple collisions
Be able to find the momentum of an object involved in a collision based on the law of conservation of momentum.
Know the difference between elastic and inelastic collisions.
F t  mv
  mv
m1v1i  m2 v2i  m1v1 f  m2 v2 f
m1v1i  m2 v2i  (m1  m2 )v f
Review Questions
1. Which has more momentum, a cheetah running at 60 miles/hour or a Greyhound bus driving at 60
miles/hour? Why?
2. Which has more momentum, a mosquito flying at 1 m/s or an elephant standing still? Why?
3. Why is it a good idea to follow through on your golf swing? How does that help you hit the golf ball
further?
4. To catch a falling person and absorb their momentum, firefighters often used to use a piece of canvas
stretched on a metal frame. A person can fall from a height of several stories and be unhurt when they
are caught like this. How is this possible? What would happen if the person landed on the sidewalk
instead?
5. As Catrina (60 kg) is flying across the continent, a small maintenance oversight leads to a window
popping out and Catrina is shoved out of the window by the pressure difference between the interior of
the cabin and the exterior atmosphere. As she falls, she quickly reaches her terminal velocity of 50 m/s
and then “coasts” down to the ground. As she nears the ground, she sees that she is falling into a
farmer’s field with a haystack, for which she tries to aim.
a) If Catrina hits the haystack, she comes to a stop in 0.08 s. How much force does the hay exert
on her to make her stop?
b) If Catrina lands in the field next to the haystack, she comes to a stop in 0.004 s. How much
force does the ground exert on her to make her stop?
c) Which way does she lose a greater amount of momentum, hitting the hay or hitting the
ground?
6. Two cars with the same mass and the same velocity are playing chicken and choose not to swerve.
They crash into each other and get tangled together. What are the cars doing after the collision?
Explain based on the law of conservation of momentum.
7. A large (100 kg) hockey player going 4.8 m/s skates into a smaller player (75 kg) who is at rest.
After the elastic collision, the smaller player is going 4 m/s. How fast is the large player moving?
8. Nick (85 kg) is standing on his skateboard (2 kg) when Alex (60 kg) runs up from behind the
skateboard at 4 m/s and jumps on. Assuming that they don’t fall off and get scraped up badly, how fast
will they be moving afterwards?
9. A small train car has a cannon mounted on it and a total mass of 6000 kg. The car is moving forward
along the tracks at 5 m/s, when the cannon accidentally discharges (good thing there were no other cars
in front of it!). A 20 kg cannonball is shot forward at 250 m/s (compared to the ground). How fast is
the train car moving after the cannonball has been fired?
10. Jeff (70 kg) takes up roller dodge ball - playing dodge ball on roller skates. He is standing perfectly
still facing north when a 1 kg ball hits him going 30 m/s to the south. After being hit, he is rolling
backwards at 0.6 m/s. What is the ball’s velocity after hitting Jeff?
11.A 20-kg toy car is moving east with a velocity of +10.0 m/s and crashes into another toy car with a
mass of 5.0 kg that is sitting at rest on a frictionless surface. If the 20.0 kg car comes to a complete stop
after collision, with what velocity does the 5.0 kg car move post-collision?
12. A 2300 kg car moving northward with a velocity of 25 m/s collides with a pole and is brought to rest
in 0.5s. Find the magnitude of the force exerted on the car during the collision.
13.A 3000-kg truck moving rightward with a speed of 5 km/hr collides head-on with a 1000-kg car
moving leftward with a speed of 10 km/hr. The two vehicles stick together and move with the same
velocity after the collision. Determine the post-collision velocity of the car and truck.
14.A 0.40 kg soccer ball approaches a player with a velocity of 18 m/s to the west. The player strikes the
ball and causes it to move east with a velocty of 25 m/s, What impulse was delivered to the ball by the
player?
15.If I wanted to apply the smallest amount of force on an object, how could I do that? Why is this
important in real life? (Provide an example of a situation in which impulse would be important). Write
in complete sentences for full credit.)