Why physics matters for RRB NTPC
Ever wonder why a train can pull a heavy carriage or how a light bulb glows? Those everyday wonders are built on the physics facts you’ll see on the RRB NTPC exam.
💡 In Simple Words: Physics is the study of how things move and interact. If you picture the world as a giant playground, physics tells you the rules for swings, slides, and seesaws. Knowing the key rules helps you solve exam problems fast.
Fundamental concepts you can’t skip
Force and motion
Force is a push or pull that can change an object’s speed or direction. Imagine pushing a shopping cart – the harder you push, the faster it rolls.
Newton’s second law (the famous F=ma) links force (F), mass (m), and acceleration (a). In plain words: heavier objects need a bigger push to speed up.
Work, energy, and power
Work happens when a force moves something over a distance. Think of lifting a box onto a shelf – you’re doing work.
Energy is the ability to do work. It comes in many flavors – kinetic (motion) and potential (stored).
Power measures how quickly work gets done. If you run up stairs faster, you’re using more power.
Simple machines
Levers, pulleys, and inclined planes are tools that let you do the same work with less effort. A seesaw is a classic lever: the longer side needs less force to lift a heavy friend.
Key formulas at a glance
Memorising the right formulas saves time. Below is a quick cheat‑sheet.
- Force: F = m × a
- Work: W = F × d (d = distance)
- Kinetic Energy: KE = ½ m v² (v = velocity)
- Potential Energy (gravity): PE = m g h (g = 9.8 m/s², h = height)
- Power: P = W / t (t = time)
- Pressure: P = F / A (A = area)
Units and conversions you’ll see
Getting the units right is a common trap. Here’s a quick reminder:
| Quantity | SI Unit | Common Symbol |
|---|---|---|
| Force | Newton (N) | F |
| Work / Energy | Joule (J) | W / E |
| Power | Watt (W) | P |
| Pressure | Pascal (Pa) | P |
Typical mistakes and how to avoid them
- Mixing up mass and weight. Mass stays the same everywhere; weight changes with gravity.
- Forgetting to square velocity in kinetic energy. It’s v², not v.
- Ignoring direction. Force and motion are vectors – they have both magnitude and direction.
- Using wrong units. Convert cm to m, grams to kilograms before plugging numbers.
Quick summary table
| Topic | Key Idea | Formula |
|---|---|---|
| Force | Push/pull changes motion | F = m a |
| Work | Force × distance | W = F d |
| Kinetic Energy | Energy of moving object | KE = ½ m v² |
| Potential Energy | Energy stored by height | PE = m g h |
| Power | Rate of doing work | P = W/t |
📝 Likely Exam Questions
- Question: A 5 kg block is pulled with a force of 20 N over a distance of 3 m. Calculate the work done.
- Answer: Work = F × d = 20 N × 3 m = 60 J.
- Question: A ball of mass 2 kg rolls down a 5‑m hill. Find its kinetic energy at the bottom (ignore friction). Use g = 9.8 m/s².
- Answer: PE at top = m g h = 2 × 9.8 × 5 = 98 J. All PE converts to KE, so KE = 98 J.
- Question: If a machine does 120 J of work in 4 seconds, what is its power output?
- Answer: Power = Work / time = 120 J / 4 s = 30 W.
- Question: A force of 15 N acts on a 3‑kg cart, causing it to accelerate. What is the acceleration?
- Answer: a = F / m = 15 N / 3 kg = 5 m/s².