Question

(a) Define the term 'work'. Write the formula for the work done on a body when a force acts on the body in the direction of its displacement. Give the meaning of each symbol which occurs in the formula.
(b) A person of mass 50 kg climbs a tower of height 72 metres. Calculate the work done. (g = 9.8 m s⁻²)

Answer 1

(a) Work is said to be done when a force causes a displacement. It is a scalar quantity that is mathematically given by the scalar product of the applied force and displacement caused. Joule is the SI unit of work. It is denoted by ‘J’.
We have a relation as,
W = FS cos θ
Where,
(F) - Force
(W) - Work
(S) - Displacement
θ - Angle between F and S
When F and S are parallel, θ = 0.
Then, work done is, W = FS

(b) Mass of the body, (m) = 50 kg
Height above the ground, (h) = 72 m
Acceleration due to gravity, (g) = 9.8 m/s²
We can calculate the work done against gravity as,
Work done in lifting a body = Weight of body × Vertical distance
So,
W = m × g × h
So work done,
W = 50 × 9.8 × 72 J
$=\boxed{35280\mathrm{J}}$
So, the work done by the man is 35280 J.