Q. A ball is projected from a certain point on the surface of a planet at a certain angel with the horizontal surface. The horizontal and vertical displacement $x$ and $y$ vary with time $t$ in second as $x = 10\sqrt{3}t$ and $y = 10t - t^{2}$ The maximum height attained by the ball is

A) 100 m
B) 75 m
C) 50 m
D) 25 m
Explanation

(d) $v_{y} = \frac{d}{dt}(y) = \frac{d}{dt}(10t) - \frac{d}{dt}\left( t^{2} \right) = 10 - 2t$
At maximum height, $v_{y} = 0$
$\therefore\ 10 - 2t = 0$ or $2t = 10$ or $t = 5$ s
$\therefore\ y = (10 \times 5 - 5 \times 5)\ m = 25\ m$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.