Question

An object with mass 5 kg is acted upon by a force, $\vec{F}=\left(-3\hat{i}+4\hat{j}\right)N$. If its initial velocity at t = 0 is $\vec{v}=\left(3\hat{i}+12\hat{j}\right)m/s$ , the time at which it will just have a velocity along y-axis is

• A. 2 s
• B. 5 s
• C. 15 s
• D. 10 s

Answer 1

Answer: (D)

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 Force along X-axis $/$ mass $=-3/5=-0.6m/s^2$
Time taken in making the velocity along $X$-axis to zero is change in velocity/acceleration $=\frac{(0-6)}{(-0.6)}=$
10 second