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

2000 J, 1000 J

Explanation

Gravitational potential is given by the expression.
W = mgh
h = Vertical displacement = 5m
m = Mass of the object = 40 kg
g = Acceleration due to gravity `= 9.8 ms^(-2)`
`:.` W = 40 xx 5 xx 9.8 = 1960 J`
At half-way down, the potential energy of the object will be 1960/2 = 980 J. At this point, the object has an equal amount of potential and kinetic energy. This is due to the law of conservation of energy. Hence, half-way dowm, the kinetic energy of the object will be 980 J.