Q. With what velocity a ball be projected vertically so that the distance covered by it in 5$^{th}$ second is twice the distance it covers in its 6$^{th}$ second ($g = 10\ m/s^{2}$)

A) $58.8\ m/s$
B) $49\ m/s$
C) $65\ m/s$
D) $19.6\ m/s$
Explanation

(c) $h_{n^{th}} = u - \frac{g}{2}(2n - 1)$
$h_{5^{th}} = u - \frac{10}{2}(2 \times 5 - 1) = u - 45$
$h_{6^{th}} = u - \frac{10}{2}(2 \times 6 - 1) = u - 55$
Given $h_{5^{th}} = 2 \times h_{6^{th}}.$ By solving we get $u = 65\ m/s$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

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