CONCEPTUAL PHYSICS: Study Guide for Chapter 7: Momentum; inertia in motion
These questions are given to you to help you focus on the
important information from chapter 7. When you can answer all of these
questions without reference to your notes or the book you are ready for the
test. If you can answer only half of these questions in this way do not expect
to pass the test! In addition to being able to answer these questions you also
need to be able to solve the PAC7 19-22 on your own without reference to your
notes or your previously done work.
does Mr. Hewitt refer to as ‘inertia in motion’?
the equation used to calculate momentum. Remember what the abbreviation
for momentum is.
how it is possible for an object with a small mass to have a very large
much momentum does an object at rest have? Use the momentum equation to
prove your answer.
7.2: Impulse Changes Momentum
- If the
momentum of an object changes what two quantities could be changing?
- If you
change your momentum which of the two quantities from #5 is changing?
- So, if
velocity changes what is required? (Remember Newton’s 2nd law!)
- If you
apply a force to make an object accelerate, does the amount of time the
force is applied matter?
happens to the change in momentum if the impulse is large; if the impulse
the equation that shows the relationship between impulse and change in
another look at the equation from #11: Show that the SI units are the same
for both sides of the equation. (I.e. show that Ns = kgm/s)
when you change momentum you are really changing velocity. So, take
another look at the equation from #11: using this equation explain how a
small force can cause a huge change in velocity.
- Why do
coaches tell their athletes to “follow through”?
let’s look at the equation from #11 from the other side: If the change in
velocity is set and cannot be changed, how can you reduce the force needed
to change the velocity?
the equation from #11 explain why you bend your knees when you jump off a
- Using the equation from #11 explain why
a class dish will break when it hits concrete but will not break when it
lands on a carpet?
boxer’s face is going to stop a punch, so the change in momentum is set in
stone. Which is it better for the boxer to do: (a) move his face into the
punch, or (b) move his face away from the punch? Using the Impulse –
change in momentum equation explain how you know.
of violent contact sports, why is the floor of a wrestling ring made of
hurts a lot to fall onto a concrete floor; it hurts less to fall on a
wooden floor. Using the equation from #11 explain why.
does it take longer to do: (a) catch something, or (b) catch something and
then throw it back?
you answer to #21: In which case is more impulse required; is which case
is the change in momentum greater?
does the Pelton Wheel do that flat water wheels can not do?
advantage does the Pelton Wheel have over flat water wheels?
7.4: Conservation of Momentum
- Is it
possible to change the momentum of your car while sitting in your car?
- Is it
possible to change the momentum of something from inside that something?
- So, to
change momentum, from where must the force come?
is the momentum of a cannonball while it is sitting inside the barrel of
is the momentum of the cannon while it is sitting on the field of battle?
- If the
momentum of the cannon-cannonball system is zero before the cannon is
fired what must the momentum of the cannon-cannonball system be after the
cannon is fired?
what is the net change in momentum of the cannon-cannonball system before
the cannon is fired and after the cannon is fired?
the cannon-cannonball system: Was any external force involved before,
during or after the cannon was fired?
you can finish this statement: If no net force or net impulse acts on a
is the only way to change the momentum of a system?
the Law of conservation of momentum.
two cars crash into each other the momentum before the collision and the
momentum after the collision must be the same; but only under what
what an elastic collision is.
- When a
collision results in the objects that collided become distorted or if heat
is generated, what kind of collision occurred?
- In our
experience perfectly elastic collisions do not happen, why not?
Hewitt claims that perfectly elastic collisions do actually occur!
Describe a perfectly elastic collision that is truly perfectly elastic.
7.6: Momentum Vectors
momentum a scalar or a vector?
the momentum of a firecracker before it explodes and after it explodes. In
one case is the momentum greater than in the other case? Explain how you