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Intro Physics
Chapter 5
Study Guide
Use your textbook to define the following terms (You may use the space below or notebook paper):
Section 5.1
1. MomentumConcept Check
Can you think of a case where a car and a truck with twice the cars mass would have the same momentum?
Section 5.2
1. impulse2. impulse- momentum relationshipConcept Check
1. If the boxer in figure 5.7 makes the time of contact 3 times as long by riding with the punch, by how
much is the force reduced?
2. I f the boxer instead moves into the punch and shortens the contact time by half, by how much is the
force increased?
3. A boxer being hit with a punch tries to extend time for best results, whereas a karate expert delivers a
force in a short time for best results. Isn’t there a contradiction here?
Section 5.3
Concept Check
1. Refer to Figure 5.8 how does the force that Cassy exerts on the bricks compare with the force
exerted on her hand?
2. How will the impulse differ if her hand bounces back when striking the bricks?
Section 5.4
1. Conserved2. Law of conservation of momentumConcept Check
A high-speed bus and an innocent bug have a head-on collision. The sudden change of momentum for
the bug spatters it all over the windshield. Is the change in momentum of the bus greater, less, or the
same as the change in momentum of the unfortunate bug?
Section 5.5
1. elastic collision
2. Inelastic collisionConcept Check
Refer to the gliders on the air track in figure 5.15 to answer these questions.
1. Suppose both gliders have the same mass. They move toward each other at the same speed and
experience an elastic collision Describe there motion after the collision.
2. Suppose both gliders have the same mass and move toward each other at equal speed. This time they
stick together when they collide. Describe their motion after the collision.
3. Suppose one of the gliders is at rest and is loaded so that it has twice the mass of the moving glider.
Again, the gliders stick together when they collide. Describe there motion after the collision.
Complete Chapter 5 Review (Pages 80-82).
More notes:
The more momentum an object has, the more difficult it is to stop.
Objects can transfer momentum to another object. Example: billiards, croquet
Elastic collisions involve objects bouncing off each other with little heat or deformation.
Inelastic collisions involve objects sticking together after a collision. This type of collision creates more heat
and deformation.
Conservation of momentum- the sum of the momentum of two objects before a collision equals the sum of
their momentums after a collision.
Sample problem: A car with a mass of 120 kg moving at a velocity of 4 m/s North crashes into a car at rest.
The car at rest has a mass of 90 kg. If the cars stick together in an inelastic collision, what is the final speed of
both cars stuck together after the crash?
v= 5 m/s
p=mv
p= 120(5)
v=0 m/s
p=mv=0
p = 90(0) = 0
p = 600 kg*m/s
p=mv
new mass is 120 + 90 = 210 kg
600 = 210v
total momentum before collision = 600 kg*m/s
Remember that the law of conservation of momentum states that the total momentum before an
interaction is the same as the total momentum after.
v = 2.86 m/s
Practice problem: A 4 kg fish is traveling 5 m/s. It swims up to and eats a 1 kg fish that was not
moving. How fast will the big fish be moving after lunch?