Core ConceptRead this first — the foundation of the topic
ENERGY
Energy is the capacity to do work. It exists in many forms but two main types dominate exams: (1) Kinetic Energy - energy due to motion = (1/2)mv², (2) Potential Energy - stored energy = mgh (gravitational). Energy cannot be created or destroyed, only converted from one form to another (Law of Conservation of Energy). Unit is Joule (J)
POWER
Power is the rate of doing work or rate of energy consumption. Power = Work/Time = Energy/Time. Unit is Watt (W). 1 Watt = 1 Joule/second. Commercial unit is kilowatt-hour (kWh). 1 kWh = 3.6 × 10⁶ J.
Formula BlockMemorise — at least one formula appears in every paper
• Work = Force × Distance (W = F × s)
• Kinetic Energy = (1/2)mv²
• Potential Energy = mgh
• Power = Work/Time = Energy/Time
• 1 HP = 746 Watts
Exam PatternsWhat examiners ask — read before attempting PYQs
RRB asks direct formula applications, unit conversions, and energy transformations. Common questions involve calculating work done against gravity, comparing kinetic energies, and power consumption problems.
ShortcutsUse these to save 30–60 seconds per question
ENERGY COMPARISON TRICK
If mass doubles, KE doubles. If velocity doubles, KE becomes 4 times (v² relationship).
2
POWER TRICK
Remember 1 HP = 746 W, 1 kWh = 36 lakh Joules
3
WORK-ZERO TRICK
Circular motion, carrying load horizontally - work done is zero
Worked ExampleSolve this step-by-step before moving on
Exam TrapsCommon mistakes students make — avoid these
#1: Students often confuse work and energy units. Both have same unit (Joule) but power has different unit (Watt). Another major error is forgetting that work done in circular motion or perpendicular direction is zero.
Many students also mix up kinetic energy formula - remember it's (1/2)mv², not mv².
REMEMBER: Energy transformations are everywhere - when you climb stairs, chemical energy converts to kinetic, then to potential energy. Exams love testing these real-life applications with numerical problems.
Key Points to Remember
Work = Force × Distance, measured in Joules (J)
Kinetic Energy = (1/2)mv², depends on velocity squared
Potential Energy = mgh, depends on height above reference point
Power = Work/Time = Energy/Time, measured in Watts (W)
1 Horsepower (HP) = 746 Watts (key conversion for exams)
A man pushes a box horizontally across a frictionless floor with a force of 50 N. The box moves a distance of 8 m in the direction of the applied force. How much work is done on the box?
Practice 2medium
A man pushes a box of mass 20 kg across a horizontal floor with a force of 100 N applied at an angle of 60° below the horizontal. The box moves 5 m. Calculate the work done by the applied force. (cos 60° = 0.5)
Practice 3hard
A 2 kg block is lifted vertically from the ground to a height of 5 m. The same block is then pushed horizontally along a frictionless surface for a distance of 10 m. If g = 10 m/s², what is the total work done against gravity during both operations?
60-Second Revision — Work, Energy & Power
Remember: Work = F × s, Energy has same unit as work (Joule)
Formula: KE = (1/2)mv², PE = mgh, Power = Work/Time
Conversion: 1 HP = 746 W, 1 kWh = 36 lakh Joules
Trap: Work done in circular motion is zero despite force application
Key: If velocity doubles, KE becomes 4 times (v² relationship)
Pattern: Energy conservation problems are 90% sure to appear
Quick check: Power questions often involve motor efficiency calculations