Transcript 332 Unit 7 Momentum student handout

Momentum
Momentum is a vector quantity
since velocity is a vector.
Impulse
Defined as a force exerted during a time period
Impulse is the cause of a change in momentum.
Elastic Cord vs a Steel Wire for
same block on frictionless surface
Elastic
Both the elastic cord & steel wire are
equal in length relaxed.
The blocks are given a quick,
equal push, sending them
sliding towards the right.
Steel
Jumping from table, mats, packaging
Compare the impulse
provided by both cord
& wire from the time
they reach their
relaxed length to when
the blocks stop.
Example
During an automobile crash test, a 1000kg car is
sent towards a cement wall at a speed of 14m/s
and is brought to a stop in 0.08 seconds.
Determine force car exerted on the wall.
Example2
A ball of mass 0.25kg is dropped from a height of
0.75m. The ball bounces back upwards from the
floor with a speed of 1.5m/s.
a) Determine the speed the ball strikes the floor prior to
bouncing back upwards.
b) Determine the impulse the ball receives from the floor.
Bus hits bug!
Who receives the greater
impulse, bug or bus?
Who receives the greater change
in momentum, bug or bus?
Who undergoes the greater
acceleration, bug or bus?
Force-time graph
A varying, onedimensional force acts
on a 50kg mass as
shown in the graph.
a) Find the magnitude of the impulse delivered to the
object.
b) Determine the change in the object's momentum.
c) If the object's original velocity was -10m/s, calculate
its final velocity.
d) What was the magnitude of the "average force" acting
on the object during the time graphed?
Stick vs Bounce + demo
Law of
Conservation of Momentum
Total momentum
before collision
equals total
momentum after
collision assuming
no external forces
acting during
collision.
3 types of collisions
• ELASTIC
• INELASTIC
• Perfectly Inelastic
‘p’ conservation equations
KE for collisions
Example
• Running at 2.0m/s, a 45-kg quarterback, collides with
a 90-kg tackle, who is traveling towards him at 7.0m/s.
Upon colliding, the tackle continues to travel forward
towards the quaterback at 1.0 m/s. Find velocity of
quarterback.
Example
During target practice, a man shoots a 7-gram bullet
with a horizontal velocity of 150 m/s directly at a 2-kg
pumpkin sitting on a post. If the bullet embeds in the
pumpkin, how fast will the pumpkin be knocked off
the post?
Example
An 88kg fullback moving east with a speed
of 5.0m/s is tackled by a 97kg opponent
running west at 3.0m/s. Assume the
collision is inelastic.
a) Find the velocity of the two immediately
after the collision.
b) Find the % of kinetic energy lost during
the collision.
Example
• Jack and Leon are fishing in their boat when they
decide to jump into the water. Jack, 45-kg, jumps off
the front of the boat with a speed of 2m/s. While at
the exact same moment, Leon, 90-kg, jumps out of the
back of the boat at a speed of 4m/s.
If the boat has a mass of 100 kg and was at rest prior to
the two boys jumping off, what will be its velocity just
after both boys have abandoned ship?
Jumping upwards
What happens to the
earth, technically
speaking, when you
jump upwards with glee
cuz you can’t wait for
physics class? Why?
The recoil momentum of a gun that kicks is ____
the momentum of the bullet it fires.