Question

A boy carrying a bag on his shoulders walking at an angle of 90 degrees does any work or not?

Answer 1

Hint:To elaborate the answer first we will define the work done by giving the daily life examples. The formula of work done we calculate that there is no work done. Then we discuss the unit of work and define it, and then talk about the angle between direction of displacement and direction of force.

Formula used:
\[W = F \times S \times {\cos ^{}}\theta \]

Complete step-by-step solution:
Work is said to be done on the object when the force acts on the object due to the cause of displacement of the object. There are three ingredient keys: force, displacement and angle between the direction of force and direction of displacement. In an order force has to qualify the work done on an object, so there must be a displacement and force must cause the displacement.
Some examples of work done observed in daily life
1. Lifting a barbell above his head by a weightlifter
2. An Olympian launching the shot-put.
 In the above example, in each case there is a force exerted upon an object to cause that object to be displaced.
The work is not to be done when the displacement is zero and also according to the Work energy theorem, work done is equal to change in kinetic energy. No change in kinetic energy is observed. So work done is zero.
In the above question \[\theta = {90^o}\]
So, by using the above formula
\[W = F \times S \times {\cos ^{}}\theta \]
\[ \Rightarrow \]\[W = F \times S \times \cos {90^ \circ }\]
\[ \Rightarrow \]\[W = F \times S \times 0\]
\[\therefore \]\[W = 0\]
Hence A boy carrying a bag on his shoulders walking at an angle of \[\theta = {90^o}\] can tell that no work is done.
The unit of work is Joule. One Joule is equivalent to one Newton of force causing a displacement of one metre.
In other words
\[1Joule = 1Newton \times 1metre\].
The change in position of an object is said to be displacement; it is as an arrow that points from the starting position to the final position.
The angle\[\theta \] is defined as the angle between the force and the displacement vector.

 Note:Work done is scalar quantity and it is the product of two vector quantities. The \[\theta \] values are depending on work and it is of three types:
1. When angle \[\theta = {0^o}\] is positive, work is said to be positive.
2. Work is said to be negative when angle \[\theta = {180^0}\]
3. Work is said to be zero when angle\[\theta = {90^0}\].