Question

10. 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.
​

Answer 1

Given:-

• Mass = 40kg
• Height = 5m

━━━━━━━━━━━━━━━

Need to find:-

• Potential energy = ?
• Kinetic Energy when it's half way down = ?

━━━━━━━━━━━━━━━

Solution:-

g = 10 m/$s^{2}$

Potential Energy = mgh

→ Potential Enegry = 40 × 10 × 5 Joules

→ Potential Enegy = 2000 Joules

━━━━━━━━━━━━━━━

At half-way down, the Kinetic energy of the item are going to be half of the total Potential Energy.

At this time, the body will have equal amount of of potential energy and Kinetic energy.

(Due to law of conservation of energy.)

Hence, half-way down, the K.E. of the object will be :-

2000 J ÷ 2

= 1000 Joules

━━━━━━━━━━━━━━━

Knowledge cell:-

• Potential energy of a particle is the energy present in a body by virtue of its state of rest.

• Kinetic Energy of a particle is the energy present in a body by virtue of its state of motion.

• Law of conservation of energy states that energy can neither be created nor destroyed. It can only be transformed from one form to another.