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 halfway down.

Mass of the object = 40kg

Height = 5m

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

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