A body with a mass of \(5\) kg is acted upon by a force \(\vec{F}=( -3\hat{i} +4\hat{j})\) N. If its initial velocity at \(t=0\) is \(\vec{v}= ( 6\hat{i} -12\hat{j} )\) m/s, the time at which it will just have a velocity along the Y-axis is:
1. never
2. \(10\) s
3. \(2\) s
4. \(15\) s

(b)
Hint: The final velocity along the x-axis is equal to zero.
Step 1: Find the acceleration of the particle.
Given, mass = 5 kg
 Acting force =F=(3i^+4j^)N Initial velocity at t=0, u=(6i^12j^)m/s Acceleration, a=Fm=(3i^5+4j^5)m/s2
Step 2: Put the final velocity along the x-axis equal to zero.
As final velocity is along Y-axis only, its x-component must be zero.
From v = u + at. As vx = 0, 
                          0=6i^3i^5t
                          t=5×63=10s