Question

An object of mass 40 kg is raised to a height of 5m 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.

Answer 1

m=40kg

h=5m

P.E.=m×g×h=40×9.8×5=200×9.8=1960J

P.E. =-1.96KJ

PE(initial)= KE(final)+PE(final)

h1=5m & h2=h1/2=2.5m

m×g×h1=KE+m×g×h2

1960-(40×9.8×2.5) =KE

KE=1960-980=980J=0.98KJ

Answer 2

the correct answer for this question is

Given:

Mass (m) = 40 kg

Acceleration due to gravity (g)= 10m/s²

Height (h)= 5m

Potential energy= m × g× h

P.E= 40 × 10 × 5 = 2000J

Potential energy = 2000J ( 2000 joules)

At a height of 5 metre object has a potential energy of 2000 J.

When this object is allowed to fall and it is Half way down its height above the ground will be half of 5 m= 5/2= 2.5m.

P.E at Half way down= m× g×h

P.E= 40× 10 × 2.5= 1000J

[h= 2.5 m]

Potential Energy at Half way down= 1000 joules.

According to law of conservation of energy:

Total potential energy= potential energy at Half way down+ kinetic energy at Half way of a down

2000 = 1000 + K.E at Half way down

K.E at Half way down= 2000- 1000= 1000J

Kinetic energy at half way down= 1000 joules.

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