Q. A body of mass $5\ kg$ starts from the origin an initial velocity $\overrightarrow{u} = 30\widehat{i} + 40\widehat{j}\ ms^{- 1}$. If a constant force $\overrightarrow{F} = - \left( \widehat{i} + 5\widehat{j} \right)N$ acts on the body, the time in which the $y -$ component of the velocity becomes zero is
A) $5\ seconds$
B) $20\ seconds$
C) $40\ seconds$
D) $80\ seconds$
Explanation
(c) $u_{y} = 40\ m/s,\ F_{y} = - 5\ N,\ m = 5\ kg$
So $a_{y} = \frac{F_{y}}{m} = - 1\ m/s^{2}$ (As $v = u + at$)
$\therefore v_{y} = 40 - 1 \times t = 0 \Rightarrow t = 40\ sec$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.