Question

A particle of mass m strikes a wall at an angle of incidence 60° with velocity V elastically. Then the change in momentum is?

Answer 1

`| Delta mathbf p| = 2 mV sin 60`

Explanation:

Check what is meant by "incident" angle. See drawing for one interpretation. Swap 30 for 60 if it's the optics definition.

For an elastic collision we can say that:

• `mathbf p_i = mV(( sin 60),(cos 60))`

and

• `mathbf p_f = mV(( -sin 60),(cos 60))`

So, kinetic energy is preserved because `|mathbf V_i| = |mathbf V_f|`

`implies | Delta mathbf p| = |mV(( - 2 sin 60),(0))| = 2 mV sin 60`