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Energy - Definition of Work

Grade 7ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Work is said to be done scientifically only when a force applied on a body produces motion in it.

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Two conditions must be met for work to be done: (1) A force must act on the object, and (2) The object must be displaced (SS) in the direction of the force.

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The amount of work done depends on the magnitude of the force (FF) and the displacement (SS) of the body.

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If a force is applied but the displacement is zero (S=0S = 0), the work done is 0 J0\text{ J}. For example, pushing a stationary wall.

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The S.I. unit of work is the Joule (JJ). It is defined as the work done when a force of 1 N1\text{ N} moves a body through a distance of 1 m1\text{ m} in the direction of the force.

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Energy is the capacity to do work. Therefore, the S.I. unit of energy is also the Joule (JJ).

📐Formulae

Work (W)=Force (F)×Displacement (S)\text{Work (W)} = \text{Force (F)} \times \text{Displacement (S)}

1 Joule (J)=1 Newton (N)×1 metre (m)1\text{ Joule (J)} = 1\text{ Newton (N)} \times 1\text{ metre (m)}

W=F×SW = F \times S

💡Examples

Problem 1:

Calculate the work done by a person who uses a force of 50 N50\text{ N} to push a trolley through a distance of 10 m10\text{ m}.

Solution:

W=F×S=50 N×10 m=500 JW = F \times S = 50\text{ N} \times 10\text{ m} = 500\text{ J}

Explanation:

The work done is calculated by multiplying the applied force by the distance moved in the direction of the force.

Problem 2:

A student exerts a force of 100 N100\text{ N} to lift a bag to a height of 1.5 m1.5\text{ m}. Find the work done.

Solution:

W=F×S=100 N×1.5 m=150 JW = F \times S = 100\text{ N} \times 1.5\text{ m} = 150\text{ J}

Explanation:

When lifting an object, the force applied is equal to the weight of the object, and the displacement is the height reached.

Problem 3:

A man pushes a heavy concrete pillar with a force of 200 N200\text{ N} for 55 minutes, but the pillar does not move. How much work is done?

Solution:

W=200 N×0 m=0 JW = 200\text{ N} \times 0\text{ m} = 0\text{ J}

Explanation:

Since the displacement (SS) is 00, the total work done is zero, despite the force and time involved.