Question

A rocket is fired upward from the earth's surface such that it creates an acceleration of $19.6m/se{c}^2$. 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 $5sec$
$v=2g\times 5=10gm/s$
Height acheived at 5 sec.$h_1=\frac{1}{2}\times 2g\times 25=245m$
On switching off the engine it goes up to height $h_2$ where its velocity
becomes zero.
$0=(10g{)}^2-2g{h}_2\Rightarrow h_2-490m$
$\therefore$ Total height of rocket =245+490=735 m