Q 11-05-030NEETJEE MainEAMCET 2009 (Engineering)Medium
A body of mass $5$ kg makes an elastic collision with another body at rest and continues to move in the original direction after the collision with a velocity equal to $\dfrac{1}{10}$ of its original velocity. The mass of the second body is
Answer: (A) $4.09$ kg
For an elastic head-on collision with a body at rest, $v_1 = \dfrac{m_1 - m_2}{m_1 + m_2}u$:
$$\frac{5 - m_2}{5 + m_2} = \frac{1}{10} \;\Rightarrow\; 50 - 10m_2 = 5 + m_2 \;\Rightarrow\; m_2 = \frac{45}{11} \approx 4.09\ \text{kg}$$
Solution by Sreeraj P, M.Sc Physics