A body with mass 5 kg is acted upon by a force `F = (3i + 4 hatj)` N. If its initial velocity at t = 0 is `v = 6i - 12hatj ms^(- 1)` , the time at which it will just have a velocity along the Y-axis is

Options

A. never
B. 10 s
C. 2 s
D. 15 s

Answer

B

Explanation

10 s
mass m = 5 kg
force = F= `(3hat(j ) + 4hat(j )) N`
Initial velocity at t=0
Acceleration `vec( a ) = (vec( F))/(m )= ((-3hat(j) + 4hat(j ))/( 5)`
`v= u + at `
`=(6hat(j) -12hat(j))+ ((-3)/( 5) hat(j ) + (4)/( 5) hat(j )) t`
Final velocity is along y -direction x - comp of final velocity = 0
`(3t)/( 5 ) =6`
`t= (5 xx 6)/(3 ) = 10 sec`