Question

A body projected vertically up with a velocity of 10 m s${}^{-1}$ reaches a height of 20 m. If it is projected with a velocity of 20 m s${}^{-1}$, then the maximum height reached by the body is :

• A. 20 m
• B. 10 m
• C. 80 m
• D. 40 m

Answer 1

The correct option is C 80 m

$u=10m{s}^{-1};h=20m$
$u_1=20m{s}^{-1};h_1=?$

Formula for maximum height

$h=\frac{u^2}{2g}$

hence

$\frac{h}{h_1}=\frac{u^2}{u_1^2};\frac{20}{h_1}=\frac{{10}^2}{{20}^2}$

$h_1=\frac{20\times 400}{100}=80m$