A light particle moving horizontally with a speed of 12 m/s strikes a very heavy block moving in the same direction at 10 m/s. The collision is one dimensional and elastic. After the collision, the particle will be

Options

A. move at 2 m/s in its original direction
B. move at 8 m/s in its original direction
C. move at 8 m/s opposite to its original direction
D. move at 12 m/s opposite to its original direction

Answer

B

Explanation

Here, `u_1 = 12 m//s , u_2 = 10 m//s`
Let `v_1` be velocity of the light particle after collision.
`v_1 = ((m_1 -m_2)u_1)/(m_1 + m_2) + (2m_2 u_2)/(m_1 + m_2) " " ……..(i)`
Given : `m_1 < < m_2`
So, `m_1` can be ignored compared to `m_2`.
From equation (i) we get , `v_1 = - u_1 + 2u_2`
Substituting the values , we get
`v_1 = -12 m//s + 2(10 m//s) = 8 m//s` in its original direction.