Question

With what speed must an object be thrown vertically upwards to reach a height of 91.5 m? (Take $g=9.8m{s}^{-2}$)

• A. 42.3
• B. 97.4
• C. 94.3
• D. 43.7

Answer 1

The correct option is A

42.3

On reaching maximum height, final velocity, $v=0,$ acceleration, $a=-9.8m{s}^{-2}$( as body is moving upwards against gravity), $s=h=91.5$ m.

Let the initial velocity be $u$

Using third equation of motion, $v^2=u^2+2as$

$0^2=u^2-2\times 9.8\times 91.5$

$u^2=1794$

$\Rightarrow u=42.3m{s}^{-1}$