Work and energy
Notes and Important notes
Class 9
Science .
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Work
Definition : Work is said to be done when a force applied to an object moves that object.
Formula : We can calculate work by multiplying the force by the movement of the object.
W = F × d
Unit: The SI unit of work is the joule (J)
Energy
Definition: In physics, we can define energy as the capacity to do work.
Formula: For the potential energy the formula is
P.E. = mgh
Unit: The SI unit of energy is joules (J), which is named in honour of James Prescott Joule.
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Answer :
Work :-
- Work is said to be done only when the force applied on a body makes the body move, i.e., if there is a displacement of the body.
- The amount of work of a body depends on two factors, i) the magnitude of force applied, ii) the displacement produced by the force.
- Work = Force × displacement of the point of application of force in the direction of force
- W = F × S (mgh)
- S.I. unit of work is joule (J).
- 1 joule = 1 newton × 1 metre.
- Work is a scalar quantity, no direction but has magnitude.
Energy :-
- The energy of a body is the capacity to do work.
- Energy spent does not depend on time.
- There is not transfer of energy is a body is acted upon by a force normal to the direction of its displacement.
- Heat energy is measured in calorie.
- S.I. unit of energy is joule (J) and C.G.S. unit is erg.
- 1 J = 10⁷ erg
- The bigger units of energy are watt hour and kilowatt hour.
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