A particle is thrown at time t = 0 with a velocity of `10 ms^(-1)` at an angle `60^@` with the horizontal from a point on an inclined plane, making an angle of `30^@` with the horizontal. The time when the velocity of the projectile becomes parallel to the incline is

Options

A. `2/sqrt3`
B. `1/sqrt3`
C. `sqrt3`
D. `1/(2sqrt3)`

Answer

B

Explanation

Taking x-axis along the inlcice and y-axis perpendicular to incline `u_(y)=10 sin (30^(@)), a_(y)=g cos (30^(@))`
When velocity becomes parallel to the inclined plane `v_(y)=0 rArr 10sin(30^(@))-g cos (30^(@))t=0 rArr t=1/sqrt3`