Transcript Momentum and Collisions

MOMENTUM AND
COLLISIONS
Momentum is similar to inertia - the tendency of an
object to remain at a constant velocity. Where as inertia
depends only on mass, momentum depends on mass AND
velocity.
Consider this:
A tennis ball traveling at 10 m/s and a medicine ball
traveling at 10 m/s. Which one is more difficult to
stop?
OK now this one:
A baseball traveling at 5 m/s and a baseball traveling at
50 m/s. Which one is harder to stop?
A force acting on a 5 kg body increases its speed
uniformly from 2.0 m/s to 8.0 m/s.
What is the initial and final momentum of the body?
What is the change in momentum?
How fast would a 125 kg object have to move to
achieve the same change in momentum?
How massive would an object be if it has the same
change in momentum when moving from 0 to 20 m/s?
Example:
A baseball pitcher hurls a 0.45 kg ball at 32
m/s. The batter crushes it and the ball leaves
the bat at 48 m/s in the opposite direction.
What was the ball’s change in momentum?
A ball is hit by a bat. The impact force is 250 N, and the
contact time is 0.2 s. What is the impulse received by
the ball?
A volleyball is spiked so that its incoming velocity of 4
m/s is changed to an outgoing velocity of 17 m/s. If the
mass of the ball is 0.6 kg, what is the impulse
provided?
How long must a 50 N force act on a 400 kg mass to
raise its speed from 10 m/s to 12 m/s?
A 1200 kg car crashes into a wall. The impulse is 4000
Ns and the impact time is 0.5 s. What is the impact
force on the car? How fast was the car going when it
hit the wall?
A 75 kg skateboarder is initially going 5 m/s to the
right. He slows to a stop over 10 seconds.
a) What is the direction and magnitude of the net force
that causes this change?
b) If the skateboarder had to stop over 2 seconds
rather than 10 seconds, what would need to be the
direction and magnitude of the net force?
c) When we changed the time over which the
skateboarder had to stop, did the impulse experienced
by the skateboarder change? Why or why not?
The Law of Conservation of Momentum
Momentum is a useful quantity because in a
closed system it is always conserved. This
means that in any collision, the total
momentum before the collision must equal the
total momentum after the collision.
pinitial = pfinal
for a collision involving two bodies,
First we are going to consider linear 1-D interactions.
There are 3 general types of these collisions:
Before
After
m1i =
m2i =
m1f =
m2f =
v1i =
v2i =
v1f =
v2f =
Before
After
m1i =
m2i =
mtotal =
v1i =
v2i =
vf
=
Before
After
mtotal =
m1f =
m2f =
vi
v1f =
v2f =
=