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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

This question has statement 1 and statement 2. Of the four choices given after the statements, choose the one that best describes the two statements.
If two springs S1 and S2 of force constants k1 and k2, respectively, are stretched by the same force, it is found that more work is done on spring S1 than on spring S2.

Statement 1: If stretched by the same amount, work done on S1, will be more than that on S2
Statement 2 : k1 < k2

  • Statement 1 is false, Statement 2 is true

  • Statement 1 is true, Statement 2 is false

  • Statement 1 is true, Statement 2 is the correct explanation for statement 1

  • Statement 1 is true, Statement 2 is true, Statement 2 is not the correct explanation for statement 1.


A.

Statement 1 is false, Statement 2 is true

As no relation between k1 and k2 is given in the question, that is why nothing can be predicted about the statement I. But as in Statment II. k1<k2
Then, for same force

straight W space equals space straight F. straight x space equals space straight F. straight F over straight k space equals space straight F squared over straight k
straight W space proportional to space 1 over straight k space straight i. straight e space for space constant space straight F
straight W subscript 1 over straight W subscript 2 space equals straight K subscript 2 over straight K subscript 1
But space for space same space displacement
straight W space equals space straight F. straight x space equals 1 half space kx. straight x space equals space 1 half kx squared
straight W space proportional to space straight K comma space straight W subscript 1 over straight W subscript 2 space equals space straight K subscript 1 over straight K subscript 2
straight W subscript 1 space less than straight W subscript 2

As no relation between k1 and k2 is given in the question, that is why nothing can be predicted about the statement I. But as in Statment II. k1<k2
Then, for same force

straight W space equals space straight F. straight x space equals space straight F. straight F over straight k space equals space straight F squared over straight k
straight W space proportional to space 1 over straight k space straight i. straight e space for space constant space straight F
straight W subscript 1 over straight W subscript 2 space equals straight K subscript 2 over straight K subscript 1
But space for space same space displacement
straight W space equals space straight F. straight x space equals 1 half space kx. straight x space equals space 1 half kx squared
straight W space proportional to space straight K comma space straight W subscript 1 over straight W subscript 2 space equals space straight K subscript 1 over straight K subscript 2
straight W subscript 1 space less than straight W subscript 2

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What is watt?

SI unit of power is Watt. 
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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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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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Define watt.

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

804 Views