Question

Two blocks of masses $m_A=10\text{kg}$ and $m_B=15\text{kg}$ initially moving in the same direction with velocities of $u_A=3\text{m/s}$ and $u_B=6\text{m/s}$ collide elastically. What is the velocity of the block of mass $10\text{kg}$ after the collision?

• A. $7.2\text{m/s}$
• B. $0.8\text{m/s}$
• C. $8.2\text{m/s}$
• D. $6.6\text{m/s}$

Answer 1

The correct option is D $6.6\text{m/s}$

We have, $m_A=10kg,m_B=15kg{u}_A=3m/s,u_B=6m/s$

Velocity of block A after collision
$v_A=\left(\frac{m_A-m_B}{m_A+m_B}\right)u_A+\frac{2m_B{u}_B}{m_A+m_B}$

$\Rightarrow v_A=\frac{10-15}{10+15}\times 3+\frac{2\times 15\times 6}{10+15}=6.6\text{m/s}$

Hence the correct option is D.