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.
Given,
Mass (m) = 40 kg
Acceleration due to gravity = 10 ms-2
Height (h) = 5 m
Potential energy = ?
We know,
Potential energy = m g h
Substituting we get,
P.E. = 40 × 10 × 5 = 2000 J
Height when halfway down : = = 2.5 m
Potential energy when halfway = ?
Substituting we get,
P.E. = 40 × 10 × 2.5 = 1000 J
According to the law of conservation of energy:
Total potential energy = potential energy halfway down + kinetic energy halfway down
2000 = 1000 + K.E. halfway down
K.E. at halfway down = 2000 - 1000 = 1000 J
Hence, Potential energy = 2000 J and kinetic energy at halfway down = 1000 joules.