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Work, Energy and Power

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Physics Part I

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Physics

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12

The sign of work done by a force on a body is important to understand. State carefully if the following quantities are positive or negative,

(e) Work done by the resistive force of air on a vibrating pendulum in bringing it to rest.


Negative Quantity.

The resistive force of air acts in the direction opposite to the direction of motion of the pendulum. Hence, negative work is done in this case.
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Define the unit joule.

Work done is said to be one joule if one newton of  force displaces the body through a distance of one meter in the direction of applied  force .
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Define watt.

Power is said to be one watt if one joule of work is done in one second. 
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What is watt?

SI unit of power is Watt. 
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Is work a scalar or a vector quantity?

Work is dot product of two vectors. i.e. F with rightwards arrow on top times S with rightwards arrow on top.

And dot product is a scalar quantity. Therefore, work is a scalar quantity. 
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What are different units of energy?

The different units of energy are :

(i) Joule            
(ii) Erg
(iii) eV            
(iv) KWh
(v) Calorie.

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