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 ela

Question

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.

TestHub · Accepted Answer

For the elastic collision between masses m and 2m, the initially stationary 2m block moves with speed

$v_{B} = \frac{2 m}{m + 2 m} (9) = 6 m/s$

It then sticks to the stationary mass m.

$(2 m) (6) = (2 m + m) v_{C}$

$v_{C} = 4 m/s$

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