Question Answers

Work, Energy & Power

1. Distinguish between conservative and non-conservative forces?

A force is said to be conservative if the workdone by the force in moving a body aroung a closed path is equal to zero. Workdone by a conservative force doesnot depends on the path taken, but depends only on the initial and final positions. For example, gravitational force, electrostatic force, etc

A force is said to be non-conservative if the workdone by the force along a closed path is not zero. Here, the workdone by non-conservative force depends on the path taken. For example, frictional force.

2. “The earth moving round the sun in an orbit is acted upon by a force, hence work must be done on the earth by this force”. Do you agree with this statement?

The earth moves around the sun in an circular orbit. The gravitational attraction force between the sun and the earth provides the required centripetal force for the circular motion of the earth. Here the displacement of the earth is perpendicular to the gravitational force. We know, $$W=F\times Scos\theta$$ The angle between the force and the displacement transverse by the earth is 90 °

So, workdone = 0

Hence, there is no workdone on the earth by the gravitational force.

3. A man carrying a bucket of water is walking on a level road with a uniform velocity. Does he do any work on the bucket while carrying it?

When a man carrying a bucket of water is walking on a level road with uniform velocity, the weight of the bucket with water acts vertically downward and the displacement is in the horizontal direction.We know, $$W=F\times Scos\theta$$ The angle between the force and the displacement transverse is 90 °

So, workdone = 0

Hence, there is no workdone on the bucket while carrying it.