Question

A stone falls freely from rest, and the total distance covered by it in the last second of its motion, equals the distance covered by it in the first three seconds of its motion. Find the time for which stone remains in the air and the total height from where stone is dropped.

• A. 5 s, 122.5 m
• B. 5 s, 222 m
• C. 6 s, 122.5 m
• D. 7 s, 122.5 m

Answer 1

The correct option is A 5 s, 122.5 m

$S_n=$ distance coveredin first $3s$

$S_n=u\times t+\frac{1}{2}\times 10\times 3^2$

Freely ball so, $u=0$

$S_n=\frac{1}{2}\times 10\times =9=45m$

$S_n=4+\frac{9}{2}(2t-1)=45$

$t=5s$ in air

$h=\frac{1}{2}g{t}^2=4.9\times 25=122.5m$