Q. Two balls of same size but the density of one is greater than that of the other are dropped from the same height, then which ball will reach the earth first (air resistance is negligible)?
A) Heavy ball
B) Light ball
C) Both simultaneously
D) Will depend upon the density of the balls
Explanation
(c) We know that gravity is a universal force with which all bodies are attracted towards the earth. Hence, g is same for both the balls. Also, if $t$ is the time taken by the balls to reach the ground, then from equation of motion.
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ s = ut + \frac{1}{2}gt^{2}$
$\Rightarrow \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ t = \sqrt{\frac{2(s - ut)}{g}}$
Since $s,\ u$ and g are same for both, hence time taken by both the balls is same.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.