A body with a mass of 55 kg is acted upon by a force F=(3ˆi+4ˆj)F=(3^i+4^j) N. If its initial velocity at t=0t=0 is v=(6ˆi12ˆj)v=(6^i12^j) m/s, the time at which it will just have a velocity along the Y-axis is:
1. never
2. 1010 s
3. 22 s
4. 1515 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=(3ˆi+4ˆj)N Initial velocity at t=0, u=(6ˆi12ˆj)m/s Acceleration, a=Fm=(3ˆi5+4ˆj5)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=6ˆi3ˆi5t
                          t=5×63=10s