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Force, Work and Energy - Concept of Work

Grade 4ICSE

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

🔑Concepts

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In science, 'Work' is said to be done only when a force applied to an object causes that object to move over a certain distance.

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Two conditions are necessary for work to be done: 1. A force must act on the object. 2. The object must move in the direction of the applied force.

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If a force is applied but the object does not move, the work done is considered zero (W=0W = 0). For example, pushing against a stationary wall results in no work.

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Work is directly proportional to both the force applied (FF) and the distance (dd) moved by the object.

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Energy is defined as the ability or capacity to do work. Without energy, we cannot apply the force required to move objects.

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The SI unit of work is the Joule (JJ).

📐Formulae

Work=Force×DistanceWork = Force \times Distance

W=F×dW = F \times d

💡Examples

Problem 1:

A boy pushes a toy car with a force of 5 N5\text{ N} and moves it a distance of 3 metres3\text{ metres}. Calculate the work done.

Solution:

W=5 N×3 m=15 JoulesW = 5\text{ N} \times 3\text{ m} = 15\text{ Joules}

Explanation:

Since the toy car moved in the direction of the force, we multiply the force by the distance to find the work done.

Problem 2:

A girl is pushing a heavy cupboard with a force of 50 N50\text{ N}, but the cupboard does not move at all (d=0d = 0). How much work is done?

Solution:

W=50 N×0 m=0 JoulesW = 50\text{ N} \times 0\text{ m} = 0\text{ Joules}

Explanation:

In science, if there is no displacement (the object doesn't move), the work done is always zero, regardless of how much force is applied.

Problem 3:

If Rahul does 20 J20\text{ J} of work by moving a box 4 metres4\text{ metres}, how much force did he apply?

Solution:

F=Wd=20 J4 m=5 NF = \frac{W}{d} = \frac{20\text{ J}}{4\text{ m}} = 5\text{ N}

Explanation:

By rearranging the work formula, we can find the force by dividing the work done by the distance moved.