A ball moving with a velocity `v` hits a massive wall moving towards the ball with a velocity a. An elastic impact lasts for time `/_\t`

Options

A. average force acting on the ball is `(2mv)/(Delta t)`
B. average force acting on the ball is `(mv)/(Deltat)`
C. kinetic energy of the ball becomes twice
D. kinetic energy of the ball remains same

Answer

A, D

Explanation

`Delta vec(P)=-m vec(v)-(m vec(v))=-2 m vec(v)`
`vec(F)=(Delta vec(P))/(Delta t) = - (2 m vec(v))/(Delta t)`
`F=(2 mv)/((Delta t))`
`K.E.=1/2m(-v)^(2)=1/2 mv^(2)`
`:.` (A) & (D)