Work

Question 1 Calculate the work done in lifting 200kg of water through a vertical height of 6 m?

Question 2 Define the term work?

Question 3 What is the S.I. unit of work?

Question 4 Is work a scalar or a vector quantity?

Question 5 Define 1 joule of work?

Question 6 What are the quantities on which the amount of work depends?

Question 7 What is the condition for a force to do work on a body?

Question 8 Write the formula for the work done on a body when a force acts on a body in the direction of its displacement?

Question 9 A load of 100 kg is pulled up by 5 m. Calculate the work done?

Question 10 If the work done by a force in moving an object through a distance of 20 cm is 24.2 J,what is the magnitude of force?

Question 11 State one example in which force does positive work?

Question 12 State one example in which force does negative work?

Question 13 State one example in which force does zero work?

Work and Energy

Work is done when a force produces motion.

For Example : When an engine moves a train along railway line, it is said to be doing work, a horse pulling the cart, a man climbing the stairs of a house, a girl pulls a trolley and it moves through a distance, lift a book through a height etc.

To do all this you apply force. Hence work is done.

The work done by a force on a body depends on
1) Magnitude of force
2) Distance through which the body moves.

Work done in moving a body is equal to the product of force exerted on the body and the distance moved by the body in the direction of force.

Work Done = Force X Distance

W= F X S

or

Work = Force X Displacement

Work done in moving a body is equal to product of force and displacement.

Work has only magnitude and no direction.

Unit of force is Newton(N) and that of distance is metre(m).

Unit of work is Newton metre or Joules(J)

When a force of 1 newton moves a body through a distance of 1 metre in its own direction,then the work done is known is known as 1 joules(J).

The S.I. unit of work is Joules. It is a scalar quantity.

The condition for a force to do work is that it should produce motion in an object.

If the distance moved is zero, then the work done on the object is always zero.

For Example :

1) A man may get completely exhausted in trying to push a stationary wall, but since there is no displacement, the work done by man on wall is zero.

2) A man standing still at bus stop with heavy suitcase in his hands may get tired son but he does no work. Because the suit case held by man do not move at all.

If the object does not move on applying force, no work is done at all.

The work done by a force can be positive, negative or zero.

1) Work done=positive , when a force acts in direction of motion of the body(displacement)

2) Work done=negative, When a force acts opposite to the direction of motion of body.

3) Work Done= Zero , When a force acts at a right angle to the direction of motion of body.
The work done on a body moving in a circular path is also zero.

To keep a body moving in a circle, there must be a force acting on it directed towards the centre. This force is called centripetal force.

When a body moves in a circular path, then centripetal force acts along the radius of circle and it is at right angle to the motion of body.

Thus work done of earth moving around sun is zero and work done in case of satellite moving round earth is zero.