Question

A ball moving with a speed $v$ hits a massive wall and returns with speed $v$. The impact lasts for time $\Delta t$, then which of the following are correct :

• A. average force acting on the ball is $\frac{2mv}{\Delta t}$
• B. average force acting on the ball is $\frac{mv}{\Delta t}$
• C. kinetic energy of the ball becomes twice
• D. kinetic energy of the ball remains the same

Answer 1

Answer: (A), (D)

The correct options are
A average force acting on the ball is $\frac{2mv}{\Delta t}$
D kinetic energy of the ball remains the same

$\Delta \overrightarrow{P}=-m\overrightarrow{v}-\left(m\overrightarrow{v}\right)=-2m\overrightarrow{v}$

$\overrightarrow{F}=\frac{\Delta \overrightarrow{p}}{\Delta t}=\frac{2m\overrightarrow{v}}{\Delta t}F=\frac{2mv}{\Delta t}$

$KE=\frac{1}{2}m{(-v)}^2=\frac{1}{2}m{v}^2$