5th Class Science Work, Force, Energy and Simple Machines Work

     Introduction

When a force is applied on a body, it may or may not move. If the applied force is sufficient to move the object from one place to another, it is said that the work has been done. If the applied force is not sufficient to move the object from one place to another, then no work has been done. Energy is the capacity to do work. In this chapter we will study about the work and energy.  

       Work

Whenever an applied force is capable to move an object, on which the force is applied, the work is done. A boy moves a chair from one place to another by applying force that means the work is done. The same boy applies a force on the wall to move it from one place to another and wall cannot move, hence, no work is done.

The following are the conditions for the work to be done:

1. A force should be applied on a body.

The body on which the force is applied should change its position.

In the picture above a body "A", moves from one place to another by the application of force. Therefore, the work is done.  

In the picture above, a man is pushing the door but the door does not change its position, hence no work is done.  

         Unit for the Measurement of Work

The unit for the measurement of work is joule which is also expressed by 'J'. The unit of work is derived from the product of applied force on a body and displacement of the body due to the applied force. Therefore, we can say that if a force of 1 N acting on a body and body moves 1 m in the direction of the applied force then 1 J of work is done. Hence, according to the work done, 1 J = 1 N (Applied force) x 1 m (Displacement) = Mm (Newton metre).

     Find the work done if a body moves through a distance of 5 m in the direction of applied force of 100 N.

(a) 500J

(b) 400J

(c) 1000J

(d) 300J

(e) None of these

Answer: (a)

Explanation 

Work done = Force x Displacement = 100 N x 5 m = 500 Nm = 500 J.

Therefore, option A is correct and rest of the options is incorrect.

      How much work is done on lifting a body of 1 kg up to the distance of 1 m above the ground or vertically?

(a) 5.6 J

(b) 2.3 J

(c) 100 J

(d) 9.8 j

(e) None of these

Answer: (d)

Explanation 

When a body of 1 kg wt. is lifted upward, it require the force of 9.8 N.

Hence, the work done = Force x Displacement = 9.8 N x l m = 9.8 Nm = 9.8 J. Therefore, option D is correct and rest of the options is incorrect.