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​

Answer 1

Solution :-

• Mass of the object = 40 kg

• Height of the object from the ground = 5 m

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

As no external force is acting on the system the total energy of the system is conserved

By applying law of conservation of energy ,

➠ KEi + PEi = KEf + PEf

here ,

• KEi = 0 ( initially the object is at rest )

• PEi = mgh = 40 x 10 x 5 = 2000 J

• PEf = mgh' = mgh /2 = 40 x 10 x 5 / 2 = 400 x 2.5 = 1000 J

Now let's substitute the obtained values in the above equation ,

➠ 0 + 2000 = KEf + 1000

➠ KEf = 2000 - 1000

➠KEf = 1000 J

The final kinetic energy of the body is 1000 J