Question

A body with mass 5 kg is acted upon by a force `vec(F) = (- 3 hat (i) + 4 hat (j)) N`. If its initial velocity at t =0 is `vec(v) = 6 hat(i) - 12 hat (j) ms^(-1)`, the time at which it will just have a velocity along the y-axis is :
A. never
B. `10s`
C. `2s`
D. `15s`

Answer 1

Correct Answer - b
Here, `m = 5kg , vec(F) = (-3hati + 4hatj)N`
Initial velocity at `t=0, vec(u) = (6hati -12hatj)m//s` retardation `hat a = vec(F)/(m) = ((-3hati)/(5) + (4hatj)/(5))m//s^(2)`
As final velocity is along Y-axis only , its x-component must be zero
From `upsilon = u +` at , for X component only `0 =6 hati - (3hati)/(5)t `
`t = (5 xx 6)/(3) =10s` .