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Momentum Word Problems

by Giggling
Tags: impulse, momentum, physics, word problem
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Jan16-11, 05:48 PM
P: 1
1. The problem statement, all variables and given/known data
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?

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

3. 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.
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Jan17-11, 04:16 AM
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tiny-tim's Avatar
P: 26,148
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
Jan17-11, 06:21 AM
P: 1,135
for 1) dont worry about the fact that then are moving on an incline ... you can always take your X axis as you need!!!

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