Work, Energy and Power

Physics Part I

Physics

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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 speedÂ *V*. If the collision is elastic, which of the following figure is a possible result after collision?Â

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.Â

For mass of each ball bearingÂ

Total kinetic energy of the system before collision,Â

=

=

Total kinetic energy of the system after collision,Â

= Â

=Â

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

CaseÂ (ii)

Total kinetic energy of the system after collision,Â

=x(2

= Â

Hence, the kinetic energy of the system is conserved in case (ii).Â

CaseÂ (iii)

Total kinetic energy of the system after collision,Â

= ()(3

= ()

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

Hence, Case II is the only possibility.

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Define the unit joule.

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

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What are different units of energy?

The different units of energy are :

(i) Joule Â Â Â Â Â Â

(ii) Erg

(iii) eV Â Â Â Â Â Â

(iv) KWh

(v) Calorie.

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