Question

A rocket is fired upward from the earth's surface such that it creates an acceleration of 19.6$m/se{c}^2$. If after 5 sec its engine is switched off, the maximum height of the rocket from earth's surface would be

• A. 245 m
• B. 490 m
• C. 980 m
• D. 735 m

Answer 1

The correct option is D 735 m

Given$a=19.6m/s^2=2g$
Resultant velocity of the rocket after 5 sec.
$v=2g\times 5=10gm/s$
Height achieved after 5 sec,$h_1=\frac{1}{2}\times 2g\times 25=245m.$
On switching off the engine it goes upto height $h_2$where its velocity
becomes zero.
$0=\left(10g^2\right)-2g{h}_2\Rightarrow h_2=490m.$
$\therefore$Total height of rocket-245+490=735m.