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Work

Component of Force

force

External force F acting on the mass m and body gets displaced by d

Force makes an angle θ with displacement

F Cosθ is the effective force on the body of mass m in the direction of the

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Definition of Work

Work W = (F cos θ )d = F . d

Work is the transferred from one object to another via the application of force along a displacement

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Positive, Zero and Negative Works

Question

Even though Work is a scalar, it can have Positive, Zero and Negative Works.

When do we say Work done is Positive ?

Hint

W = (F cos θ )d = F . d

Cos180 = -1, Cos90 = 0 and Cos0 = +1

Answers

Force or component of force is in the direction of displacement

Force is in the direction perpendicular to the displacement

Force or component of force is opposite direction of displacement

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Question

When do we say Work done is Zero ?

Hint

W = (F cos θ )d = F . d

Cos180 = -1, Cos90 = 0 and Cos0 = +1

Answers

Force or component of force is in the direction of displacement

Force is in the direction perpendicular to the displacement

Force or component of force is opposite direction of displacement

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Question

When do we say Work done is Negative ?

Hint

W = (F cos θ )d = F . d

Cos180 = -1, Cos90 = 0 and Cos0 = +1

Answers

Force or component of force is in the direction of displacement

Force is in the direction perpendicular to the displacement

Force or component of force is opposite direction of displacement

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True-False Question

Question 1

A work done by friction is always negative

Hint

Friction opposes relative motion

Question 2

 When you jump, work done by gravity is positive

Hint

Gravity opposes

Question 3

Work done by any centripetal force is zero

Hint

Force is radial, displacement is tangential