Question

Give five examples of zero work.

Answer 1

Hint: Firstly, we will define zero work, then, we will use the formula that relates the work done, force applied, the displacement and the angle between the force applied and the displacement to mathematically represent the zero work. Finally, continue with some examples.
Formula used:
\[W=Fs\cos \theta \]

Complete answer:
The formula that relates the work done, force applied, the displacement and the angle between the force applied and the displacement is given as follows.
\[W=Fs\cos \theta \]
Where F is the force applied, s is the displacement and \[\theta \] is the angle between the force applied and the displacement.
When the angle between the force applied and the displacement is zero, then the work done will be,
\[\begin{align}
  & W=Fs\cos \theta \\
 & \Rightarrow W=Fs\cos 0{}^\circ \\
 & \therefore W=Fs \\
\end{align}\]
Thus, there will be work done, and the value of this work done equals the value of force times the displacement.
When the angle between the force applied and the displacement is\[90{}^\circ \], then the work done will be,
\[\begin{align}
  & W=Fs\cos \theta \\
 & \Rightarrow W=Fs\cos 90{}^\circ \\
 & \therefore W=0 \\
\end{align}\]
Thus, the value of work done will be zero and this work is called the “zero work”.
The examples of this type of work, that is zero work are:
The normal force or the gravitational force acting downwards. This force acts perpendicular to the surface of the earth.

While walking a man holding an object.
The displacement of a person running forward on a horizontal surface.

(The gravitational force will be perpendicular).

Man pushing the vertical wall. (The force applied by the man will be perpendicular).
Sleeping on a horizontal bed.

(The gravitational force will be perpendicular).
\[\therefore \]The work done is said to be zero when the displacement and the force will be perpendicular to each other.

Note:
We can consider any example for zero work, the only condition to remember while forming the examples is that the force applied should be perpendicular to the displacement. There will be work done but gets cancelled out by the perpendicular force.