Key Formulas for Work, Energy, and Power in Class 9 Physics

Work done by a constant force:

• W = F × s

Where:

• W = Work done (Joule, J)
• F = Force applied (Newton, N)
• s = Displacement of the object in the direction of the force (meter, m)

Kinetic energy of a moving object:

• KE = 1/2 × m × v²

Where:

• KE = Kinetic energy (Joule, J)
• m = Mass of the object (kilogram, kg)
• v = Velocity of the object (meter/second, m/s)

Potential energy of an object at a height:

• PE = m × g × h

Where:

• PE = Potential energy (Joule, J)
• m = Mass of the object (kilogram, kg)
• g = Acceleration due to gravity (approximately 9.8 m/s²)
• h = Height of the object above the ground (meter, m)

Law of Conservation of Energy

• Total energy of an isolated system remains constant:
• Initial total energy = Final total energy
• Kinetic energy + Potential energy = Constant

Power:

• P = W / t

Where:

• P = Power (Watt, W)
• W = Work done (Joule, J)
• t = Time taken (second, s)