## abdul_shabeer 3 years ago A body of mass M collides against a wall with velocity V and rebounds with the same speed. It's change of momentum is

No Change as such

2. hkaur

momentum= mass*velocity both remain same after collision so no change in momentum.

3. abdul_shabeer

But how? Are we to add both the momenta?

5. salini

adarsh see the direction change as well first it is +v next it is -v

Okay. yeah, got it. First, Its MV. Second is -MV. Subtracting, we get 2MV.

7. abdul_shabeer

By subtracting how we get 2MV

But I don't understand why the sign is +ive in first case and -ive in second case.

See, MV - ( - MV) = MV + MV = 2MV(Simple integer addition)

Can anyone say about the signs?

11. salini

|dw:1329838538143:dw|because we shud maintain a standard sign system like think this way

So, in all physics problems requiring direction, we need to follow Cartesian System, rite?

13. salini

yeah there is more than that for that u need to come to 11th for now understand that when it is a 1-dimensuional(straight line motion) follow the co-ordinate axes