Revision: Work, Energy and Power Physics HSC Science Class 11 Tamil Nadu Board of Secondary Education

Power is defined as the rate of doing work or work done per second.

i.e., Power = `("Work done in joule")/("Times in second")`

or,  p = `("W (in joule)")/("t (in second)")`

The rate of doing work is called power.

For two colliding bodies, the negative of the ratio of the relative velocity of separation to the relative velocity of approach is called the coefficient of restitution.

A collision in which linear momentum is conserved but kinetic energy is not conserved is called an inelastic collision.

A collision in which both linear momentum and kinetic energy are conserved is called an elastic collision.

A collision as a process where "several objects come together, interact (exert forces on each other) and scatter in different directions."

OR

An event where two or more bodies exert forces on each other in a relatively short time is called a collision.

OR

The interaction between two bodies during a very small duration in which they exert relatively large forces on each other, and during which momentum or kinetic energy is transferred from one object to another, is called Collision.

Power P = \[\frac{\text{Work done }W}{\text{Time taken }t}\]

or

P = \[\frac {W}{t}\]

• S.I. unit: If 1 joule of work is done in 1 second, the power spent is said to be 1 watt.
• C.G.S. unit: The C.G.S. unit of power is erg per second (erg s^-1).
• Relationship between S.I. and C.G.S. units:
   1 W = 1 J s^-1 = 10⁷ erg s^-1
• 1 horse power (H.P.) = 746 W = 0.746 kW