A particle is thrown at `t = 0`, with an initial velocity `sqrt(11)hat(i)+35hat(j)`, where `hati` is along horizontal & `hat(j)` is along vertically upward direction. The acceleration due to gravity is `10 m//s^(2)` in invertically downward direction. The time instant(s) at which the speed of the particle becomes `6 mm/s` is//are

Options

A. `3` sec
B. `2` sec
C. `5` sec
D. `4` sec

Answer

A, D

Explanation

Along `x-` direction `v_(X) = u_(X) + a_(X)t`

`6cosalpha = sqrt(11) rArr cos alpha = (sqrt(11))/(6), sinalpha = (5)/(6)`
Along `y-`direction `6sin = 35 - 10t`
`rArr t = 3 sec`.
Also `-6 sin theta = 35 - 10t`
`rArr t = 4 sec`