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 ` [i.e. COM is rest]
`X_("COM") = (m_1 x_1 + m_2x_2)/(m_1 + m_2) = (m xx 0 + 2m (60))/(m + 2m) = 40 m`