Question

A body $P$ moving with a velocity of $20$ms${}^{-1}$ collides with another body $Q$ of same mass at rest. After collision $P$ comes to rest. What is the velocity of the body $Q$ ?

• A. $10$ms${}^{-1}$
• B. $20$ms${}^{-1}$
• C. $30$ms${}^{-1}$
• D. $5$ms${}^{-1}$

Answer 1

Answer: (B)

$20$ms${}^{-1}$

By using momentum conservation,we get,
$m_1{u}_1+m_2{u}_2=m_1{v}_1+m_2{v}_2$
But $m_1=m_2=m,u_1=20$ms${}^{-1},u_2=0$ms${}^{-1},v_1=0$ms${}^{-1},v_2=?$
$\Rightarrow m\times 20+m\times 0=m\times 0+m\times v_2$
$\Rightarrow v_2=20$ms${}^{-1}$.