PhysicsA body with mass 5kg is acted upon by a force f=(−3i^+4j^)N. If its initial velocity at t=0, v=(6i^−12j^)ms−1, the time at which it will just have a velocity along the y axis is

A body with mass 5kg is acted upon by a force $f = (- 3 \hat{i} + 4 \hat{j}) N$ . If its initial velocity at t=0, $v = (6 \hat{i} - 12 \hat{j}) {ms}^{- 1}$ , the time at which it will just have a velocity along the y axis is

A
15 sec
B
10 sec
C
2 sec
D
Never

Solution:

When the body has velocity along y-axis its velocity along the X-axis becomes zero then V_x = 0

$\begin{aligned} V_{x} & = u_{x} + a_{x} t \\ = u_{x} + \frac{F_{x}}{m} t \\ 0 & = 6 \hat{i} - \frac{3 \hat{i}}{5} t \\ \Rightarrow & 3 t = 30 \\ \Rightarrow & t = 10 \sec \end{aligned}$