Question

Define work. Give its S.I unit. Write an expression for positive work done.

Answer 1

Work can be calculated in relation to force and displacement. It is a process of energy that is transferred to an object by applying force. Work is done only if there is a displacement produced due to the force. The SI unit of work is given in joule (J).

Complete step by step solution:
If a body is acted upon by a force, then its work done is found by the product of the magnitude of this force and displacement of the body affected by the force. Significantly, displacement happens in the procedure. If there is no displacement, the work done will be zero. Displacement due to a force will be in any direction. When force is applied to an object, a component of force either horizontal or vertical, will be present in the same direction of displacement or in the opposite direction. Positive work happens if the direction of displacement is towards the direction of the force. Negative work happens if the direction of displacement is towards the opposite of the direction of the force.
Now, the equation of work can be given as
$W = F \times d$
Here,
$F$ is the force applied to a body
$d$ is the displacement of the body affected by the force
$W$ is the work done by the force $F$on the body
Force is applied at an angle $\theta$to the displacement, work done is given by
$W = Fd\cos \theta$
This equation is the general expression of work.
The SI unit of work is $joule(J)$. Sometimes $joule(J)$ is also stated as $newton - metre(N.m)$.

Note:
If an object is pulled through a distance of $8m$on a horizontal surface by acting a force of $10N$ and $\theta$ is $0$ and $\cos \theta = 1$ Work done in this situation is given as$W = Fd\cos \theta = Fd(1) = Fd = 10N \times 8m = 80J$. This problem proves that $Fd\cos \theta$ can be applied in any condition and it is the general expression for work done.