A particle of mass m strikes a wall at an angle of incidence 60° with velocity V elastically. Then the change in momentum is?
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))#
#mathbf p_f = mV(( -sin 60),(cos 60))#
So, kinetic energy is preserved because