Question

15-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 9m/s and makes an elastic collision with it. Thereafter, B makes completely
inelastic collision with C. All motions occur on the same straight line. The final speed of
the object C is​

Answer 1

Answer:

4 m/s

Explanation: For perfectly elastic and inelastic collision conserve momentum and energy.

Answer 2

Given :

mass of A = m

mass of B = 2m

mass of c = m

velocity of A = 9 m/s

To find :

The final speed of C .

Solution :

let the velocity after the collision be va , vb , vc .

on conserving momentum for 1st collision , we get ,

va + 2 vb = 9     .....(i)

on conserving energy for the 1st collision , we get ,

va^2 + 2 vb^2 = 81       ......(ii)

by (i) and (ii) ,

vb = 6 m/s

The second collision is perfectly inelastic . So , after the collision the bodies will attain same velocity and move as one body .

on conserving momentum , we get ,

2m * vb = (2m + m) * vc

vc = (2/3) * vb

=> vc = 4 m/s

The final speed of  the object C is​ 4 m/s .