Work is done when a force causes displacement in the direction of the force. Mathematically, W = F·d·cos ?, where is the angle between force and displacement. Work is measured in Joules (J).
Kinetic Energy (KE) is the energy possessed by a body due to its motion. KE = ½mv², where m is mass (kg) and v is velocity (m/s). A moving roller-coaster cart at the bottom of a hill has maximum KE.
Potential Energy (PE) is stored energy due to position. Gravitational PE = mgh, where g = 9.8 m/s² and h is the height above reference level. At the top of a hill, the cart has maximum PE.
Conservation of Energy (NCERT Class 11 Ch. 6): In an isolated system, total mechanical energy remains constant: KE + PE = constant. When friction is present: KE + PE + Heat = Total Energy (constant). This is the first law of thermodynamics applied to mechanics.
Power is the rate of doing work: P = W/t = F·v. Unit: Watt (W). A 100 W bulb consumes 100 J every second.
Key Formulas
Quantity
Formula
Unit
Work
W = F·d·cos?
Joule (J)
Kinetic Energy
KE = ½mv²
Joule (J)
Potential Energy
PE = mgh
Joule (J)
Power
P = W/t = Fv
Watt (W)
CBSE Exam Tip: The work-energy theorem states that the net work done on an object equals the change in its kinetic energy: W_net = ?KE. This is one of the most frequently tested concepts in CBSE Class 11 and JEE Physics.