Q. If we throw a body upwards with velocity of $4m/s,$ at what height does its kinetic energy reduce to half of the initial value?
(Take $g = 10 ms^{- 2}$

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A

$4m$

B

$2m$

C

$1m$

D

$0.4m$

Solution:

Initial kinetic energy of the body
$=\frac{1}{2}mv^{2}=\frac{1}{2}m\left(\right.4\left(\left.\right)^{2}=8m$
Let at height $h,$ the kinetic energy reduces to half,
i.e., it becomes $4m.$
It is also equal to potential energy.
Hence, $mgh=4m$ or $h=\frac{4}{ g}=\frac{4}{10}=0.4m$

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