Momentum and Collisions: Solving for Post-Collision Velocities

[Giggling]

Homework Statement

1. Joe is sledding down a snow hill when he collides with Mike half way down the hill. Joe and the sled have a mass of 65 kg and their velocity before the collision was 12 m/s. If Mike has a mass of 55 kg, what velocity would Joe, Mike, and the sled have after the collision?

2. A 3 kg cart is moving along when it strikes a 2 kg cart (initially at rest). The velocity of the two-cart combination after the collision is 4 m/s. Calculate the velocity of the 3 kg cart before the collision.

3. Tyler is standing at the 10-yard line waiting to catch the initial kick-off. The .75 kg football experiences a change in velocity of 12 m/s in .17 s when caught by Tyler. What force does Tyler apply on the football?

Homework Equations

P = mv
I = F * (change in time) = m(final velocity)- m(initial velocity)

The Attempt at a Solution

1. I know that.. mass 1 = 65 kg, mass 2 = 55 kg, velocity 1 = 12 m/s
But I don't know what equation to use.. Or what needs to be found.

2. I got 6.7 m/s, I am not sure if it's correct
(3kg * velocity 1) + (2kg * 0 m/s) = (3kg * 4m/s) + (2kg * 4m/s)

3. No idea.. But I did find that the change in time is .17 s and the mass is .75 kg and I think the final velocity is 12m/s. But I don't know what equation must be used.

 

[tiny-tim]

Welcome to PF!

Hi Giggling! Welcome to PF!

Your 2. is correct.

Now do 1. exactly the same way … you can assume that the two sleds carry on together just like the two carts.

For 3., you need to apply the full version of good ol' Newton's second law … force = rate of change of momentum

 

[cupid.callin]

for 1) don't worry about the fact that then are moving on an incline ... you can always take your X axis as you need!