Question 126 of 130

A moving particle of mass $m$, makes a head on elastic collision with another particle of mass $2 m$, which is initially at rest. The percentage loss in energy of the colliding particle on collision, is close to

A$33 \%$B$67 \%$C$90 \%$D$10 \%$

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Answer: (C) $90 \%$

Fractional decrease in kinetic energy of mass $m$
$$\begin{aligned} & =1-\left(\frac{m_2-m_1}{m_2+m_1}\right)^2=1-\left(\frac{2-1}{2+1}\right)^2 \\ & =1-\left(\frac{1}{3}\right)^2=1-\frac{1}{9}=\frac{8}{9} \end{aligned}$$