Edexcel M1 Impulse question

I don't really get the impulse stuff in M1 (Edexcel)...
Like for this question (June 2005, q's 2) , I did part a), but for part b), I'm not sure about the direction of the impulse and have got quite a few of these kind of questions wrong...
Could someone explain impulse and momentum please?

Two small steel balls A and B have mass 0.6 kg and 0.2 kg respectively. They are movingtowards each other in opposite directions on a smooth horizontal table when they collidedirectly. Immediately before the collision, the speed of A is 8 m s–1 and the speed of Bis 2 m s–1. Immediately after the collision, the direction of motion of A is unchanged and thespeed of B is twice the speed of A. Find
(a) the speed of A immediately after the collision,(5)
(b) the magnitude of the impulse exerted on B in the collision. (3)

Hi!

All impulse is is the change in momentum.

So in this question, to find the impulse exerted on B, you use the equation:
$I = m(v-u),[br][br]where I is impulse,[br]m is mass of the object,[br]v and u are the final and initial velocities respectively.$

Can you try the question now?

Hope I helped.

I got this question correct , as I took rightwards as the positive direction and then did
$I=0.2(8.8--2)[br]=0.2(10.8)[br]=2.16 Ns.$

For a different question though (January 2005, q's 1c), I did the same thing, but got -8.25 Ns as the impulse, when the answer should just have been 8.25 Ns...do you know why I got the wrong answer?

If the question simply asks for the magnitude of the impulse, just write down the positive of whatever your answer is if you come out with a negative.

Okay, thanks