Question

A body of mass 10 kg projected vertically upward from the ground has potential energy 580 joules and kinetic energy 1380 joules at a certain point in its path. The velocity of projection of the body must be

• A. $16.6m{s}^{-1}$
• B. $19.8m{s}^{-1}$
• C. $14m{s}^{-1}$
• D. $10.8m{s}^{-1}$

Answer 1

Answer: (B)

$19.8m{s}^{-1}$

K.E at point of launch $=$ total M.E. (since these as no P.E at launch)
$=580+1380$ (since there is no non-conservation force, so ME is conserved)

$\Rightarrow \frac{1}{2}m{v}^2=1960$

$\Rightarrow v^2=\frac{1960}{5}$

$\Rightarrow v=19.8m/s$