Question

A body with mass 5 kg is acted upon by a force F = ( -3 $\hat{i}$ + 4 $\hat{j}$)N. If its initial velocity at t=0 is v = ( 6 $\hat{i}$ - 12 $\hat{j}$)m$s^{-1}$, 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

Answer: (B)

10 s

Our interest is in finding the moment when the velocity along X-axis becomes zero. So noting the initial velocity along X-axis as $u=6m/s$

Acceleration along X-axis is $\text{Force along X-axis}/mass=-3/5=-0.6m/s^2$

Time taken in making the velocity along X-axis to zero is $\text{change in velocity}/acceleration=\frac{(0-6)}{(-0.6)}=10second$