# Change in momentum?

ok so my physics textbooks crap, it explains something in a tiny paragraph without any examples (I'm getting new ones). I have this question I'm stuck on. There is 2 balls that both have the mass of 1.5kg, one is not moving and one is moving at 4m/s - so ball A is about to collide with ball B. the questions are: the momentum of ball A just after collision, momentum of ball B just after collision and velocity of ball B after the collision?

do I use force= change in momentum/time taken for the change equation. so for the first two im guessing the question is to find the change in momentum which is force x time taken for change. but what is the time taken for the change - is it 4m/s???? or do I need a different equation to find out the time it took for the change and then use that to find out the change in momentum?

What is the resultant force on BOTH balls when they collide with each other?

What is the resultant force on BOTH balls when they collide with each other?

I don't know, all the information for the question I have is what I have given...

.... oh... under the question theres another line that says, 'after the collision both balls move to the right but the velocity of ball A is now 1m/s

... I should be able to figure out these questions now, I think... maybe if you could do the first for me? so I have something to work from, as I have no example to get an idea with.

when the two balls collide with each other, ball A gives a force to ball B and ball B gives an equal and opposite force to ball A. Hence the resultant force on the two balls taken together is zero.

Hence momentum is conserved.

i.e. initial momentum = final momentum.

Try to work out this equation and you get the answer required.