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. 10 s
C. 2 s
D. 15 s

Answer 1

Correct Answer - B
Given ,mass m = 5 kg
Acting force = F = `(-3 hati + 4 hatj) N`
Initial velocity at t = 0 . U = `(6hati - 12 hatj) m//s `
Retardation , `hata = (F)/(m) = (-(3hati)/(5) + (4hatj)/(5)) m//s^(2)`
As final velocity is along Y-axis only , its x-component must be zero.
From v = u + at , for X - component only 0 = `6 hati - (3)/(5)t`
`t = (5 xx 6)/(3) = 10 s`