Two particles one of mass m and the other of mass 2 m are projected horizontally towards each other from the same level at a distance of 60 m velocities `10 ms^(-1)` and `5 ms^(-1)` respectively. They collide in air and stick to each other. The distance from A, where the combined mass forms is ....... m.

Options

A. zero
B. `20`
C. `30`
D. `40`

Answer

D

Explanation

`vec(V)_("com") = (m_1v_1 + m_2v_2)/(m_1 + m_2) = (m(10) + 2m (-5))/(m + 2m) = 0 " " ` [ie, COM is at rest]
`X_("com") = (m_1 x_1 + m_2 x_2)/(m_1 _ m_2) = (m xx 0 + 2m(60))/(m + 2m) = 40 m`