WORK, ENERGY AND POWER
Frequently Asked Questions
Work is said to be done when a force produces displacement in the direction of the force.
Work = Force × Displacement × cos?
Because it has magnitude only and no direction.
Work is positive when force and displacement are in the same direction.
Work is negative when force acts opposite to displacement.
Work is zero when displacement is zero or force is perpendicular to displacement.
Centripetal force in uniform circular motion does zero work.
A force whose magnitude or direction changes with displacement.
By finding the area under the force–displacement graph.
Energy is the capacity to do work.
Joule (J).
The sum of kinetic energy and potential energy.
Energy possessed by a body due to its motion.
KE = ½ mv²
Mass of the body and square of its velocity.
Energy possessed by a body due to its position or configuration.
Energy due to height in a gravitational field.
PE = mgh
Energy stored in a stretched or compressed elastic body.
Force is directly proportional to extension within elastic limit.
PE = ½ kx²
A force whose work is path independent.
Gravitational force, spring force.
A force whose work depends on path followed.
Friction, air resistance.
Net work done equals change in kinetic energy.
W = ?KE
It provides an alternative method to solve motion problems.
Energy can neither be created nor destroyed, only transformed.
When only conservative forces act.
When non-conservative forces like friction act.
Freely falling body under gravity.
Conversion of energy from one form to another.
Electrical to mechanical in motors.
Rate of doing work.
P = Work / Time
Power at a particular instant.
P = F · v
Watt (W).
A non-SI unit of power (1 hp ˜ 746 W).
Commercial unit of electrical energy.
Energy.
Ratio of useful output energy to input energy.
Efficiency = (Output/Input) × 100%
Due to energy losses like heat and friction.
It converts mechanical energy into heat.
Because it is perpendicular to velocity.
Distance covered before a moving body comes to rest due to braking.
Work–energy theorem.
It links kinematics and dynamics and is widely used in numericals.
