Q. A body of mass 500 g is thrown upward with a velocity $20{ms}^{- 1}$ and reaches back to the surface of a planet after 20 s. Then the weight of the body on that planet is
A) 2 N
B) 4 N
C) 5 N
D) 1 N
Explanation
(d) Here, $u = 20\ {ms}^{- 1},\ m = 500g = 0.5kg,\ t = 20\ s$
Using Newton’s equation of motion
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ s = ut + \frac{1}{2}{gt}^{2}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 0 = 20 \times 20 + \frac{1}{2}( - g)(20)^{2}$
$or\ \ \ \ \ \ \ \ \ \ \ \ g = 2\ ms^{- 2}$
$\therefore\ \ Weight\ of\ body\ on\ planet = mg$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 0.5 \times 2 = 1\ N$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.