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)
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
Related Questions
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(a) State the freezing temperature of the liquid.
(b) Name the phase change happening at the region QR.
(c) In which state (solid / liquid) does the above substance liberate heat at a faster rate? Justify.
The diagram shows a wheel with a handle. Two forces, F1 and F2 of equal magnitudes are acting on the handle as shown in the diagram.
(a) Which force produces negative moment?
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A ball of mass 20 g falls from a height of 45 m. It rebounds from the ground to a height of 40 m. Calculate :
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(b) the speed of the ball at which it hits the ground.
(c) the loss in kinetic energy on striking the ground.
[g = 10 m s-2]
To lift a load of 30 kgf, Suhas uses a single fixed pulley while Radha uses a single movable pulley. The displacement of efforts in both the cases are equal. In an ideal situation calculate the ratio of :
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(b) the potential energy gained by the loads in the two cases.
(c) the efficiencies in the two cases.