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. [3 MARKS]

Answer 1

Each point: 1 Mark

1. Gravitational potential energy is given by the expression,
W = m g h
Where,
h = Vertical displacement = 5 m
m = Mass of the object = 40 kg
g = Acceleration due to gravity = $9.8m{s}^{-2}$
$\therefore W=40\times 5\times 9.8=1960J.$

2. At half-way down, the potential energy of the object will be $\frac{1960}{2}=980J$.

3. 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 down, the kinetic energy of the object will be 980 J.