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Force, Work and Energy - Work and its definition

Grade 5ICSE

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 on an object causes it to move through a certain distance in the direction of the force.

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Two conditions are essential for work to be done: (1) A force must be applied to the object, and (2) The object must move or change its position (s≠0s \neq 0).

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If a force is applied but the object remains stationary (e.g., pushing a heavy wall), the distance moved is 00, and therefore the work done is also 00.

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The amount of work done depends on the magnitude of the force applied and the distance through which the object moves.

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

📐Formulae

Work=Force×DistanceWork = Force \times Distance

W=F×sW = F \times s

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

💡Examples

Problem 1:

A girl applies a force of 20 N20\text{ N} to push a toy car across the floor for a distance of 5 m5\text{ m}. Calculate the work done by the girl.

Solution:

W=20 N×5 m=100 JW = 20\text{ N} \times 5\text{ m} = 100\text{ J}

Explanation:

Using the formula W=F×sW = F \times s, we multiply the force (20 N20\text{ N}) by the distance (5 m5\text{ m}) to find that 100 Joules100\text{ Joules} of work was performed.

Problem 2:

Rohan pushes against a large boulder with a force of 50 N50\text{ N} for ten minutes, but the boulder does not move. How much work is done?

Solution:

W=50 N×0 m=0 JW = 50\text{ N} \times 0\text{ m} = 0\text{ J}

Explanation:

Since the distance moved (ss) is 0 m0\text{ m}, the product of force and distance is zero. Scientifically, no work is done if there is no displacement.