Finding impulse on particle A in collision when only one mass is known

[thomas49th]

Homework Statement

Two particles A and B, of mass 0.3 kg and m kg respectively, are moving in opposite
directions along the same straight horizontal line so that the particles collide directly.
Immediately before the collision, the speeds of A and B are 8 m s–1 and 4 m s–1 respectively.
In the collision the direction of motion of each particle is reversed and, immediately after
the collision, the speed of each particle is 2 m s–1. Find:

a) the magnitude of the impulse exerted by B on A in the collision

Homework Equations

I = m(v-u)

The Attempt at a Solution

How do i know what mass to use? the mass m or 0.3? Is there a rule?

Thanks :)

 

[Gib Z]

Well. I = Ft, and by Newtons Third law, the magnitudes of the Forces should be negatives of each other, and the time of contact is obviously the same for both. Also, due to the Conservation of Momentum, I, which is just change in momentum, but also be the same magnitude for both particles.

So basically, really, it doesn't matter which you sub in because you are to get the same value, but since you don't actually know the value of m, putting that into the equation won't give an answer, though putting in 0.3 will.

From the previous information, you should now be able to determine m.

 

[thomas49th]

Ahh i can use either ball. I see :)

I can get m easy.

Thank you very much :)