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Question

# (a) What happens to the work done when the displacement of a body is at right angles to the direction of force acting on it ? Explain your answer. (b) A force of 50 N acts on a body and moves it a distance of 4 m on a horzontal surface. Calculate the work done if the direction of force is at an angle of 60∘ to the horizontal surface.

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Solution

## a- No work is done. Work involves the dot product of force and displacement, which means you have to consider the angle between them. W=→F⋅→x=Fxcosθ See that cosine term? If the angle between the force and displacement is ninety degrees then the work done is zero. Now, it seems like you may have been asking “where does the work go?”. You have to understand that in such a case, no energy is being transferred. The work isn’t “going” anywhere because there isn’t any work at all. b- Work done = 50 ×4 cos 60° = 200×1/2 Work done = 100 J

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