Three identical spherical balls A, B and C are placed on a table as shown in the figure along a straight line. B and Care at rest initially. 

The ball A hits B head on with a speed of `10 ms^(-1)`. Then after all collisions (assumed to be elastic) A and B are brought to rest and C takes off with a velocity of 

Options

A. `5 ms^(-1)`
B. `10 ms^(-1)`
C. `2.5 m s^(-1)`
D. `7.5 ms^(-1)`

Answer

B

Explanation

Since A, B and C are identical balls, if any of the two balls undergo elastic collision, they will exchange their velocities.

Thus, when A and B collide, A comes to rest, and B start moving ahead with `10 ms^(-1)` .
Similarly, when B collides with C , B comes to rest and C starts moving ahead with a speed of `10 ms^(-1)`.