Two particles are simultaneously projected in the same vertical plane from the same point with velocities u and v at angles `alpha and beta` with horizontal. Find the time that elapses when their velocities are parallel.

Answer

A, B, C

Explanation

`v_1 = (u cos alpha)hati + (u sin alpha-g t)hatj`
`v_2 = (v cos beta)hati + (v sin beta - g t)hat j`
These two velocity vectors will be parallel when,
the ratio of coefficients of `hati` and `hatj` are equal.
`:. (u cos alpha)/(v cos beta) = (u sin alpha - g t)/(v sin beta - g t)`
Solving we get ,
` t = (uv sin (alpha-beta))/(g(v cos beta - u cos alpha))`.