1. Aim: How can we account for direction with momentum conservation?
HW: Problem Set

2. Car Collision
If the car and truck below collided, which direction would the two cars move. Be sure to explain your answer in terms of momentum.

3. Summary
Collision! What happens if the balls are Elastic? How about completely inelastic? How can we demonstrate using dynamic carts?

4. 1D Elastic collisions with carts
When we play a game of pool with pool balls, what is conserved?
KE and momentum
Therefore, we can use both equations concerning an objects motion or collision.
By combining equations we have:
vA – vB = v’B – v’A
Students are expected to describe a pool ball’s motion at slides end. How does the balls motion change upon contact if both are elastic? Velocity of ball A drops to zero and ball B gains that velocity. Energy conserved!

5. Inelastic Collisions with carts
What are some good examples?
Two objects that collide and stick together are totally inelastic.
Our cart has a mass:
If we measure a constant velocity (repeated every push), how will it change for an inelastic collision with another cart?
What does this mean in terms of energy?
Push cart with constant velocity alone and measure its velocity… V
Push cart at same speed into another cart and record new Velocity V’
What is the change in energy? How much was lost in collision? KE = .5mv2

6. Practice

7. A 95 kg fullback is running at 4 m/s to the east and is stopped in
A 95 kg fullback is running at 4 m/s to the east and is stopped in .75 seconds by a head on tackle by a tackler heading west.
Original fullback momentum?
Impulse exerted on fullback?
Impulse exerted on tackler?
Average force exerted on tackler?
380 kg m/s East
380 kg m/s West
F = ΔP/Δt = 507 N East

8. Calculate the force and direction exerted on a rocket given that the propelling gasses are expelled at a rate of 1500 kg/s with a speed of 4 x 104 m/s at the moment of takeoff. F = ΔP/Δt = vΔm/Δt F = 6 x 107 Downward Force on rocket is Newton’s 3rd law force pair! F = 6 x 107 Upward!

9. Summary
In terms of energy, how is an elastic collision different from an inelastic one?
Is momentum a vector or scalar? Why?
Today we discussed 1D momentum, what do you think is next???