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Question 13 Marks
(a) What is energy? State and define SI unit of energy.
(b) Define potential energy with an example.
(c) Define kinetic energy with an example
Answer
(a) The capacity of a body to do work is called energy. SI unit of energy is joule. When one newton force causes a displacement of one metre in its own direction, the energy spent is said to be one joule.
(b) Potential energy is the amount of energy possessed by a body by virtue of its position or configuration.
Example : When the spring of a watch is wound, its configuration changes. Thus, the spring possesses potential energy
(c) Kinetic energy is the energy possessed by a body by virtue of its motion.
Example: Energy possessed by a train moving on rail track.
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Question 23 Marks
(a) Define work.
(b) What are the conditions for doing work?
(c) State the mathematical expression for work.
Answer
(a) Work is said to be done only when the force applied on a body causes a displacement of the body in the direction of force or any resolved component of the force.
(b) Conditions for doing work:
(i) There must be a force acting on the body.
(ii) The force acting on the body must cause a displacement.
(iii) The displacement must be in the direction of force or its resolved component.
(c) Mathematically, work is the product of force and the displacement in the direction of force.
$W =\overrightarrow{ F } \overrightarrow{ S }= FS \cos \theta$ (if force acts at angle $\theta$ with horizontal)
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[3 Mark Question Answer] - Physics STD 10 Questions - Vidyadip