Three objects $A,B$ and $C$ are kept in a straight line on a frictionless horizontal surface. These have masses $m,\ 2m$ and $m$ respectively. The object $A$ moves towards $B$ with a speed $9\ m/s$ and makes an elastic collision with it. Thereafter, $B$ makes completely inelastic collision with $C$. All motions occur on the same straight line. Find the final speed (in $m/s$) of the object $C$ [image:6_image22.emf]

Question

Dr. Abubacker · Accepted Answer

(b) [image:6_image79.emf]
$v_{2} = \frac{2m_{1}v_{1}}{m_{1} + m_{2}} = \frac{2 	imes m 	imes 9}{m + 2m} = 6\ m/s$
$i.e.$ After elastic collision $B$ strikes to $C$ with velocity of $6\ m/s$. Now collision between $B$ and $C$ is perfectly inelastic
[image:6_image80.emf]
By the law of conservation of momentum
$2m 	imes 6 + 0 = 3m 	imes v_{sys}$
$\Rightarrow v_{sys} = 4\ m/s$

Explanation

Reviewed by Dr. Abubacker

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