Q. A stone is shot straight upward with a speed of $20\ m/sec$ from a tower 200 $m$ high. The speed with which it strikes the ground is approximately
A) $60\ m/sec$
B) $65\ m/sec$
C) $70\ m/sec$
D) $75\ m/sec$
Explanation
(b) Speed of stone in a vertically upward direction is $20m/s$. So for vertical downward motion we will consider $u = - 20\ m/s$
$v^{2} = u^{2} + 2gh = ( - 20)^{2} + 2 \times 9.8 \times 200 = 4320\ m/s$
$\therefore v \simeq 65m/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.