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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
Two identical ball bearings in contact with each other and resting on a frictionless table are hit head-on by another ball bearing of the same mass moving initially with a speed V. If the collision is elastic, which of the following figure is a possible result after collision? 



The total momentum before and after a collision in each case is constant.

For an elastic collision,

Total kinetic energy of a system remains conserved before and after the collision. 

For mass of each ball bearing m, we can write, 

Total kinetic energy of the system before collision, 

= 1 halfmV2 +1 half(2m) × 02
=1 halfmV2

Case (i)

Total kinetic energy of the system after collision, 

= 1 half m × 0 +1 half (2m) (straight V over 2)2
=open parentheses 1 fourth close parentheses mV2
Hence, the kinetic energy of the system is not conserved in case (i).

Case (ii)

Total kinetic energy of the system after collision, 

=open parentheses 1 half close parenthesesx(2m) × 0 + 1 halfmV2 
= 1 half mV2
Hence, the kinetic energy of the system is conserved in case (ii). 


Case (iii)

Total kinetic energy of the system after collision, 

= (1 half)(3m)(straight V over 3)2
= (open parentheses 1 over 6 close parentheses)mV

Hence, the kinetic energy of the system is not conserved in case (iii). 

Hence, Case II is the only possibility.
180 Views

Define watt.

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

What is watt?

SI unit of power is Watt. 
773 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