Solving an Elastic Collision Problem with Given Force-Time Data

[the7joker7]

Homework Statement

A 10-kg mass moving at a speed of V_{1} in a positive direction collides elastically with a 2-kg mass which is initially at rest. The magnitude of the net force that acts on each object during the collision is shown in the figure. Find the initial velocity, V_{1}, of the 10-kg mass prior to collision, the final velocity, v_{3}, of the 10-kg mass, and the final velocity, v_{4}, of the 2-kg mass.

I can't post the figure up, but it's a force with respect to time chart. It starts with nothing, then starts to spike upwards at a constant rate from time 1 millisecond to time 3 milliseconds, where it peaks at 10000N, then goes back down at the same rate, hitting 0N at 5 milliseconds. I've already figured the Impulse is 20 N*s from this.

Homework Equations

p = mv

I = F/deltaT

/deltap = mv_{final} - mv_{initial}

mv_{before collision} = the some of mv_{after collision}

Possibly assorted others.

The Attempt at a Solution

So far, I know the Impulse is 20 NS.

Impulse = Momentum, I do believe.

So

20 = (10)V

Making Velocity of the first object initially = 2 m/s, correct?

That would answer the first question, but I'm not totally sure where to go from there.

 

[the7joker7]

Here's a quick idea of what I tried to do...lemme know if it looks right.

20 = (10)V_{3} + 2(V_{4})
20 = .5(10)V_{3}^{2} + .5(2)V_{4}^{2}

Those are the conservation of momentum and energy equations.

I solved the momentum one for V_{3} and got .55279 m/s. I can post steps if anyone wants to see.

Then I plugged that into the energy one and got 1.7061 m/s. Sound about right?

It looks like it MIGHT be accurate, but the sums of mv before and the sums of mv after aren't equal.

I got 2(10) = 20 for before and 10(.55279) + 2(1.7061) = 8.94 for after. =/

 

[physixguru]

my answers:

v1 + V3 = 10
2V1 = 12
V1 = 6 m/s
V3 = 4 m/s

 

[the7joker7]

How is V1 6m/s?

Am I doing the impulse equation wrong?