Question

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An object of mass 40 kg 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.


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Answer 1

Answer:

Given :

Mass of the object M=40kg

Height upto which it is raised h=5 m

Potential energy P.E=Mgh

P.E=40×10×5=2000J

Let its kinetic energy be E

k

when it is half way down i.e h

′

=

2

h

According to conservation of energy,

K.E

i

+P.E

i

=K.E

f

+P.E

f

0+2000=E

k

+Mg

2

h

∴ 2000=E

k

+40×10×

2

5

⟹E

k

=1000J

Answer 2

Answer:

Given

Mass of the object = 40kg

Height = 5m

Find out

We need to find Potential energy and also its kinetic energy when it is half-way down

Solution

Potential energy (K.E) is given by the expression,

K.E = m × g × h

Where,

m = Mass of the object

h = Vertical displacement

g = Acceleration due to gravity (9.8 ms-2)

P.E = 40 × 9.8 × 5

P.E = 1960 J

At half-way down, the Kinetic energy of the item:

At this time, the item has an equal quantity of potential and K.E.

This can be due to law of conservation of energy. Hence, half-way down, the K.E. of the object can be calculated as

1960 J/ 2

⇒ 980 J

half way down = 980 J

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