Physics
(a) Name the unit of work done, used in subatomic scale.
(b) To which class of lever does a pair of scissors belong?
(c) A stone is tied to a string and displaced from A to B by application of constant force F in three different ways as shown in the diagram below.
Arrange the three cases in ascending order of the work done by the force. (Given AJB is a semi-circle, θ < 90° and AB = 20 m)
Work, Energy & Power
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Answer
(a) electron volt (eV)
(b) Class I lever
(c) Given,
- AJB is a semi-circle.
- θ < 90°
- AB = 20 m
Work done by a force is given by
W = Force x Displacement x cos θ,
where θ is the angle between force and displacement.
- Case 1 : The stone moves along a semicircular path, so the force is always perpendicular to the direction of displacement which makes θ = 90°.
Hence, work done is zero.
- Case 2 : The force acts along the direction of displacement from A to B, so θ = 0°.
Hence, work done is maximum.
- Case 3: The force acts at an angle θ < 90° to the displacement, so only the component Fcosθ does work.
Hence, the work done is less than Case 2 but more than Case 1.
Therefore, the ascending order of work done is Case 1 < Case 3 < Case 2
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