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i cant understand negative work done..

Dear Student!

When the direction of displacement and force are opposite, i.e. are at angle of 180°, work done is said to be negative. For example, when an object is lifted up away from the surface of Earth, work done by the gravitational force is negative as displacement is upwards while force is acting downward.

Mathematically, work done is given as, W = F.d.cos θ, where, F is the force, d displacement, and θ is the angle between the direction of force and displacement.

When the value of θ is 180°, cos 180° = -1(by trigonometry), thus work done becomes negative.

Hope this is useful to you!

Regards

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View Full Answer

When the direction of the force (F) applied and displacement (s) are opposite to each other, then the work done is said to be negative.

This means that S and F are anti parallel to each other. The angle between them is 180 Degree.

Examples : - 1) When we pull water from a well the displacement and gravitational force are opposite to each other. So, the work done by them is negative.

2) Work done by fricitonal force is always negative. 

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are u sure with the second example  what u hav given???

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