An object of Mass $40 k g$ is raised to a height of $5 m$ above the ground what is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half way down.

Question

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Answer 1

Given :
Mass of the object $M = 40 k g$
Height upto which it is raised $h = 5$ m
Potential energy $P . E = M g h$
$P . E = 40 \times 10 \times 5 = 2000 J$

Let its kinetic energy be $E_{k}$ when it is half way down i.e $h^{'} = \frac{h}{2}$
According to conservation of energy,
$K . E_{i} + P . E_{i} = K . E_{f} + P . E_{f}$
$0 + 2000 = E_{k} + M g \frac{h}{2}$
$∴$ $2000 = E_{k} + 40 \times 10 \times \frac{5}{2}$
$⟹ E_{k} = 1000 J$

Answer 2

Given :

Mass of the object

M = 40 k g

Height upto which it is raised

h = 5

m

Potential energy

P . E = M g h

P . E = 40 \times 10 \times 5 = 2000 J

Let its kinetic energy be

E_{k}

when it is half way down i.e

h^{'} = \frac{h}{2}

According to conservation of energy,

K . E_{i} + P . E_{i} = K . E_{f} + P . E_{f}

0 + 2000 = E_{k} + M g \frac{h}{2}

∴

2000 = E_{k} + 40 \times 10 \times \frac{5}{2}

⟹ E_{k} = 1000 J