Download The more momentum an object has, the more difficult it is to stop

CHAPTER FIVE NOTES - EXPLORATIONS TEXT
Momentum = Mass x Velocity
p = mv
The more momentum an object has, the more difficult it is to stop.
I = Ft = Δ mv
Impulse = Force x time = change in momentum
When stopping an object, the impulse will be the change in momentum and therefore will
be the same number regardless of the time involved. However, the force can change
drastically depending upon the amount of time in which the object is brought to a halt.
As the length of time is increased, the force decreases. In stopping an object, force and
time are inversely proportional. Damage is generally much less if the time to stop or
slow an object is increased.
Sample impulse problem: If a 65 kg cart (with a velocity of 12 m/s) is brought to a stop
in 1 second, how much force will be exerted?
Impulse = Ft = Δ mv
1
F = 780 Newtons
I = 65 x 12 - 0 = 780
780 = Ft
780 = F x
How much force would be required if the stopping time were 4 seconds?
Impulse is the same as before I = 780
F = 195 N
I = Ft
so
780 = F x 4
Conservation of momentum- the total momentum of two objects before a collision
equals the total momentum 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
total momentum before collision = 600 kg*m/s
p=mv
new mass is 120 + 90 = 210 kg
600 = 210v
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
Elastic collision- collisions with no lasting deformation of objects and no appreciable
heat. The objects bounce off each other. Example: Billiard balls
Inelastic collisions- collisions where there is heat, deformation of objects, or both.
Objects stick together. Example: Cars stick together on impact and get dented
(depending upon the materials and impact force).
The more momentum an object has, the more difficult it is to stop.
Objects can transfer momentum to another object. Example: billiards, croquet
Practice problems:
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?
A 2 kg piece of putty moving 2 m/s crashes into a 1 kg toy car and they stick
together. How fast are they moving after the crash?
A 3 kg cart moving 4m/s crashes into and sticks to a 1 kg cart at rest. How
fast are they moving after the crash?
An astronaut with a mass of 50 kg is at rest in the middle of a room in the
space station (his is floating). He throws a 1 kg ball 12 m/s and then he begins
to move in the opposite direction at a speed of _____________.