Lesson 7, Topic 1
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# The Concept of Work

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### Topic Content:

• Definition of Work
• Work done = F × d
• Work Done on an Object at an Angle
• Proof that Work done = F d cos θ
• Work Done When a Body is Lifted
• Work done = mgh

When a man moves from one point to another carrying a load, the man has performed work, but when a boy carries a load for 2 hours without moving from one point to another, no work has been done. Therefore, for work to be done, force must be applied to a body through a particular distance.

In the illustration above, the work done is the product of the force (12 N) used to push the box and the distance (5 m).

Therefore, work is said to be done whenever a force moves a body through a distance in the direction of the force.

Or

Work is defined as the product of the force and its perpendicular distance moved in the direction of the force.

Work done = force × distance in the direction of the force

= force (f) × displacement (d)

= Newton × metre

= Nm

Also, Remember that Force = mass × acceleration

Therefore, Work done can also be written as:

mass × acceleration × displacement

The S.I unit of work is Joule (J) or Newton metre (Nm)

### Example 7.1.1:

A man applied a force of 20 N to a cart which moved through a distance of 15 m. Calculate the work done by the man.

Solution:

F = 20 N, distance = 15 m

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#### Responses

1. Thanks a lot, nice one