Calculating change of momentum during an impact

Momentum is mass multiplied by velocity (speed) - so the change in momentum is (mass x speed) afterwards minus the (mass x speed) before. So if the mass is 10kg and the speed before is 10m/s, and the speed after is 12m/s then, mass x speed after = 10x12=120 Kg m/smass x speed before = 10x10=100 Kg m/sSo change in momentum is 120-100=20 Kg m/sGood luck!

thank you. What happens if I am given no initial velocity. For example I have this question:

A molecule of mass 5.0*10-26kg moving at a speed of 420ms-1 hits a surface at right angles to the surface and rebounds at the same speed in the opposite direction in an imoact lasting 0.22ns
I'm given the mass and speed, but not the initial speed. How do I work it out?

Momentum is mass multiplied by velocity (speed) - so the change in momentum is (mass x speed) afterwards minus the (mass x speed) before. So if the mass is 10kg and the speed before is 10m/s, and the speed after is 12m/s then, mass x speed after = 10x12=120 Kg m/smass x speed before = 10x10=100 Kg m/sSo change in momentum is 120-100=20 Kg m/sGood luck!