Q 11-05-099JEE MainJEE Main 2023 (25 Jan, Shift 2)Easy
A body of mass $1\ \text{kg}$ collides head on elastically with a stationary body of mass $3\ \text{kg}$. After collision, the smaller body reverses its direction of motion and moves with a speed of $2\ \text{m s}^{-1}$. The initial speed of the smaller body before collision is ______ $\text{m s}^{-1}$.
Numerical value type. Enter your answer.
Answer: 4
For an elastic collision with the target at rest: $v_1=\dfrac{m_1-m_2}{m_1+m_2}u=\dfrac{1-3}{4}u=-\dfrac u2$.
$\dfrac u2=2\Rightarrow u=4\ \text{m s}^{-1}$.
Solution by Sreeraj P, M.Sc Physics