Question

Explain the work done in following cases
a. When person is standing is a place holding a suitcase in his hand.
b. when he is moving holding the suitcase In his hand.

Answer 1

ANSWER :

( a ). When a person is standing in a place holding a suitcase, then no work will be done because, work done = force × displacement. So, here force acts perpendicular and no displacement because person doesn't move, So work done will be 0.

( b ). If he is moving holding a suitcase then the work will be done.

Answer 2

The work done in the mentioned cases will be as mentioned below:

In the first case,

When the person standing in a place holding a suitcase in his hand, the work done on the system = 0

We know, Work done on a system = Force acting on the system × net displacement of the system

Here, if the person is standing in a place holding his suitcase in his hand, so the displacement will be 0.

So, in this case the work done will also be 0.

In the second case,

The man is moving holding the suitcase in his hand.

So, the displacement of the man has a value, if it is s, then,

The Work done by gravity on the man will be = F.s

Here, the force, F = mg is acting in perpendicular to the displacement. [ m= mass of the man, g= acceleration due to gravity]

According to the formula of work done, W = F. s

                                                                 ⇒ W = Fs Cos θ

                                                                ⇒ W = Fs Cos 90

                                                                ⇒ W = 0 [As Cos 90 = 0]

So, the work done = 0