Question

d. Calculate the energy stored in a body of mass 40 kg when it is at a height of 30m.

The right answer is 11760


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Answer 1

mgh = ↓

mass × gravitational field × height

40 × x × 30 = 1,200

g = 11760 ÷ 1200

= 9.8

proof :-

40×9.8×30 = 11760

here g was not given , so I did like this if here g was given I would simply multiply.

Answer 2

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