The velocity vector of a sphere after it hits a vertical wall which is pallel to `hatj` is `(-hati + 3hatj)` on a smooth horizontal surface. The coefficient of restitution between ball and wall is `(1//2)`. Final the velocity vector of sphere immediately before collision.

Options

A. `hati + 3 hatj`
B. `-2 hati + 3 hatj`
C. `-hati + 3 hatj`
D. `2 hati + 3 hatj`

Answer

B

Explanation

Component of velocity parellel to wall will remain unchanged. `(3 hatj)` willl remain same . `(hati)` component
will become `(- hati) xx (-(1)/( e)) = (- hati) (-2)`
Velocity vector of sphere immediately before collision
`=2 hati + 3 hatj`