Q- Give one example of:-
- positive work done
- negative work done
- zero work done
Examples of positive work:
(1)Pushing a book on a table to some distance
(2)Lifting a bucket of water
(3)Pulling a box on the floor to another place
(4)Climbing a tree
(5)Kicking a football
Examples of negative work:
(1)The work done by the frictional force, when we push the book to a distance.
(2)The work done by the gravitational force, when we are lifting a bucket of water from the well.
(3)The work done by the gravitational force, when we are climbing on a tree.
(4)The work done by the frictional force of air, when a ball is falling downwards.
(5)The work done by the buoyant force, when a coin is sinking.
Examples of zero work:
(1)If we push a wall, the wall remains unaltered. The work done by us on the wall is zero
(2)If a person is walking horizontally with a load on his head, then the work done by the person against gravity is zero.
(3)The work done against gravity in moving a book horizontally on a table is zero.
(4)If we try to move a heavy box, and the box is not at all moving, then the work done by us will be zero.
(5)The centripetal force acting on an object under circular motion does zero work on the object.
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Wok done is said to be positive when the displacement is in direction of applied force. Ex : When you push a box it move forward. Here thework done is positive in accordance with the force you applied.
Work done is said to be negative when the displacement is opposite to the direction of the force applied. Ex : When brakes are applied o moving vehicle, it movesforward some distance although the force applied is in the direction opposite to which the vehicle is moving. Therefor the work done is said to be negative.
Work done is said to be zero when the displacement is perpendicular to the direction of force applied. Ex : When a person is walking forward with a load on his head, he is doing zero wok on the object in terms of gravity.