A body of mass 5 kg statrs from the origin with an initial velocity `vec(u) = (30 hat(i) + 40 hat(j)) ms^(-1)`. If a constant force `(-6 hat(i) - 5 hat(j))N` acts on the body, the time in which they component of the velocity becomes zero is

Options

A. `5s`
B. `20 s`
C. `40 s`
D. `80 s`

Answer

C

Explanation

Here, `vecu = 30 hati +40 hatj ms^(-1) , m=5 kg,`
`vecF=-6hati-5 hatj N` .
`therefore ` Acceleration,` a =( VecF)/(m ) = (- 6 hati - 5 hatj )/( 5) =- (6 hati )/( 5) - hatj ms^(-2)`
The y component of velocity at any time t is given by
` v_y = u_y + a_y t = 40 - 1(t)`
According to the given problem, `v_y = 0 `
`therefore t= 40 s`