Question

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.​( g = m/s² )​

Answer 1

We know

PE = mgh

= 2000J

According to law of conservation of energy Potential energy at halfway will be equal to kinetic energy at half way.

So

mgh/2 = KE

= 1000J

Answer 2

Given:

• Mass,m = 40 kg

• Acceleration due to gravity, g = 10 m/s²

• Height, h = 5 m

To find out:

Find potential energy and kinetic energy when it is half-way down.

Solution:

We know that,

Potential energy ( at 5 m height) = m × g × h

= 40 × 10 × 5

= 400 × 5

= 2000 J

When the object is allowed to fall and its half away down,

Height = 1/2 × 5 = 2.5 m

Potential energy ( at 2.5 m height ) = m × g × h

= 40 × 10 × 2.5

= 1000 J

Now,

According to the law of conservation of energy:

Total P.E = P.E at half way down + K.E at half way down

⇒ 2000 = 1000 + K.E at half way down

⇒ K.E at half way down = 2000 - 1000

⇒ K.E at half way down = 1000 J