Momentum & Impulse: Find Average Force in Elastic Collision

[mizzy]

Homework Statement

A locomotive of mass 21x10^3kg traveling at 2.0m/s runs into an identical stationary locomotive.

If the collision is perfectly elastic and lasts for 1.5s, find the average force exerted on the stationary locomotive during the collision.

Homework Equations

Find momentum before and after the collision (m1v2 + m2v2 = m1v2 + m2v2)

Use impluse to find the average force (F = p/t)

The Attempt at a Solution

I found the momentum before and after the collision.

For the second part, I'm not sure which momentum to use. The final one?

Can someone tell me if I'm right?

 

[Doc Al]

Use impluse to find the average force (F = p/t)

That should be F = Δp/t.

For the second part, I'm not sure which momentum to use. The final one?

You need the change in momentum.

 

[mizzy]

the change in momentum after the collision?

 

[Doc Al]

the change in momentum after the collision?

Change = Final - Initial

I guess the initial momentum of the stationary locomotive was zero; so you're OK with using the final momentum.

 

[mizzy]

Thanks