Download 02.Notes-2015-MomentumImpulsewithProblems

Momentum – ________________________________________________________________
Equation:
Units:
Example:
A 1180 kg car drives along a street at 30.0 mph. A major-league pitcher can
give a 0.142 kg baseball a speed of 101 mph. What speed in (mph) must the
baseball have if its momentum is to be equal in magnitude to that of the car?
Momentum changes all the time!
Equation:
Examples:
• A car slowing down
• A tennis ball coming into the racket at one speed and leaving at another
• A golf ball being hit off the tee
Impulse – How do you slow/stop a car or hit a tennis ball, etc.? You exert an impulse! This is the force
you apply over the time you apply it and it is EQUAL to the object’s change in momentum!
Impulse Equation:
Impulse = Change in Momentum
I  p
Therefore:
Example:
A 0.25 kg softball moving at 22 m/s is hit by a bat into the outfield at 19 m/s. The contact time between
the ball and the bat is 0.16 seconds.
a. What is the change in momentum?
b. What is the impact force of the bat on the ball?
c. What is the impact force of the ball on the bat? (Think Newton!)
* For a fixed change in momentum (as
in during a crash or collision when
going from high speed to rest),
sometimes it is advantageous to
increase the time of impact in order to
decrease the force:
Hockey – Receiving a pass
_____ time
_____ force
Circus – Safety net
_____ time
_____ force
Air bags in cars
_____ time
_____ force
*When you want to want to change the momentum of something such as a
baseball or golf ball that is initially at rest to give it a large final speed, you want
to exert as large of a force as possible over a long amount of time:
Baseball – following through
_____ time and force _____ velocity
Golf Swing – following through _____ time and force
_____ velocity
* And even other times, what you can control is the speed (or change in speed)
and this can produce a large force!
Karate – breaking brick with bare hands
____ velocity _____ force
The “Rebound” Concept: The diagram to below depicts the before and after collision speeds of a car
which undergoes a head-on-collision with a wall. In Case A, the car bounces off the wall. In Case B,
the car crumples up and sticks to the wall. Assuming the mass of the car and its contact time with the
wall in each situation are the same,
a. Which case results in the greatest change in velocity?
b. Which case results in the greatest acceleration?
c. Which case results in the greatest change in momentum?
d. Which case results in the greatest impulse?
Momentum and Impulse Practice 1
Concepts:
1. When a golfer uses a large force and follows through with the ball on his tee off, does this increase
or decrease the impulse? Does this increase or decrease the momentum of the ball?
2. In a car crash, why are air bags advantageous?
3. Do you experience an impulse if you:
a. throw a ball?
b. catch a ball?
c. catch a ball, then throw it out again?
In which of the above cases is the impulse the greatest? Why?
4. When you ride a bicycle at full speed, which has the greater momentum, you or the bike? Use this to
help explain why you go over the handlebars if the bicycle is brought to an abrupt halt.
Problems:
5. A 0.060-kg tennis ball traveling at 10.0 m/s is returned by Serena Williams. It leaves her racket
with a speed of 36.0 m/s in the opposite direction from which it came.
a. What is the change in momentum of the tennis ball?
b. If the ball is in contact with the racket for 0.020 s, with what average force has Serena hit the
ball?
6. Wayne hits a stationary 0.12-kg hockey puck with a 240 N force that makes the puck shoot across
the ice with a speed of 20.0 m/s scoring a goal for the team. How long was Wayne’s hockey stick in
contact with the puck?
7. Deanne hits a 0.050-kg golf ball, giving it a speed of 75 m/s. What impulse does she impart to the
ball?
Momentum and Impulse Practice 2
1. Jim strikes a 0.058 kg golf ball with a force of 272 N and gives it a velocity of 62 m/s. How long was the club
in contact with the ball?
2. A force of 186 N acts on a 7.3 kg bowling ball for 0.4 s.
a. What is the bowling ball’s change in momentum?
b. What is its change in velocity?
3. A 5500 kg freight truck accelerates from 4.2 m/s to 7.8 m/s in 15 s by applying a constant force.
a. What change in momentum occurs?
b. How large is the force exerted?
4. A 0.24 kg volleyball approaches Zima with a velocity of 3.8 m/s. Zima bumps the ball, giving it a velocity of 2.4 m/s. What average force did she apply if the interaction time between her hands and the ball is 0.025 s?
5. A 0.145 kg baseball is pitched at 42 m/s. The batter hits it horizontally to the pitcher at 58 m/s.
a. Find the change in momentum of the ball.
b. If the ball and bat were in contact for 0.0005 s, what would the force of the bat on the ball?
6. A 550 kg car traveling at 24 m/s collides head-on with a 680 kg pick-up truck. Both vehicles come to a
complete stop upon impact.
a. What is the momentum of the car before the collision?
b. What is the change in the car’s momentum?
c. What is the change in the truck’s momentum?
d. What is the velocity of the truck before the collision?