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Work, Energy and Power

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Physics Part I

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Physics

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Class 10 Class 12

A ball is thrown vertically downwards from a height of 20m with an initial velocity vo, It collides with the ground, loses 50% of its energy in collision and rebounds to the same height. The initial velocity vo is,
(Take g = 10 ms-2)

  • 14 ms-1

  • 20 ms-1

  • 28 ms-1

  • 10 ms-1


B.

20 ms-1

Suppose a ball rebounds with speed v,


straight v space equals space square root of 2 gh space end root space equals space square root of 2 space straight x space 10 space straight x space 20 space end root space equals space 20 space straight m divided by straight s

Energy space of space straight a space ball space just space after space rebound comma

straight E space equals space 1 half space mv squared space equals space 200 space straight m

As comma space 50 space percent sign space of space energy space loses space in space collision space means space just space before space collision space energy space 400 space straight m.
According space to space law space of space conservation space of space energy comma space we space have
1 half space mv subscript 0 superscript 2 space space plus space mgh space equals space 400 space straight m

rightwards double arrow space 1 half mv subscript 0 superscript 2 space plus space straight m space straight x space 10 space straight x space 20 space equals space 400 space straight m space
rightwards double arrow space straight v subscript straight o space equals space 20 space straight m divided by straight s

Suppose a ball rebounds with speed v,


straight v space equals space square root of 2 gh space end root space equals space square root of 2 space straight x space 10 space straight x space 20 space end root space equals space 20 space straight m divided by straight s

Energy space of space straight a space ball space just space after space rebound comma

straight E space equals space 1 half space mv squared space equals space 200 space straight m

As comma space 50 space percent sign space of space energy space loses space in space collision space means space just space before space collision space energy space 400 space straight m.
According space to space law space of space conservation space of space energy comma space we space have
1 half space mv subscript 0 superscript 2 space space plus space mgh space equals space 400 space straight m

rightwards double arrow space 1 half mv subscript 0 superscript 2 space plus space straight m space straight x space 10 space straight x space 20 space equals space 400 space straight m space
rightwards double arrow space straight v subscript straight o space equals space 20 space straight m divided by straight s

7781 Views

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 .
799 Views

What are different units of energy?

The different units of energy are :

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

804 Views

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. 
1450 Views

Define watt.

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

What is watt?

SI unit of power is Watt. 
773 Views