Question

A sphere of mass m, moving with a speed v, strikes a wall elastically at an angle of incidence $\theta$. If the speed of the sphere before and after collision is the same and the angle of incidence and velocity normally towards the wall the angle of rebound is equal to the angle of incidence and velocity normally towards the wall is taken as negative then, the change in the momentum parallel to wall is :

• A. mv cos $\theta$
• B. -2mv cos $\theta$
• C. 2mv cos $\theta$
• D. zero

Answer 1

Answer: (D)

since the sphere collided elastically and there was no friction there was no impulse on the sphere along the wall.The only contact force acted was normal and that obviously was perpendicular to surface. NO change in momentum parallel to wall.