Why physics matters for RRB NTPC
Imagine a train speeding up, a lamp lighting up, or a ball bouncing – all of those are physics in action, and the exam loves them.
💡 In Simple Words: Physics is the study of how things move and interact. For the RRB NTPC exam you just need to remember a handful of facts, formulas, and everyday examples that turn tricky questions into easy ones.
Important physics facts for RRB NTPC
Units and measurements you can’t ignore
Unit means the standard way we measure something, like metres for length or seconds for time. The SI system (International System of Units) is the official set used in Indian exams.
- Length – metre (m)
- Mass – kilogram (kg)
- Time – second (s)
- Force – newton (N). A newton is the push needed to give a 1‑kg mass an acceleration of 1 m/s², like the gentle nudge you give a shopping cart.
Key formulas you’ll see
Write these on a sticky note and keep it on your study desk.
- Speed (v) = Distance (s) ÷ Time (t)
- Acceleration (a) = Change in speed ÷ Time
- Force (F) = Mass (m) × Acceleration (a) – think of it as "how hard you push".
- Work (W) = Force (F) × Displacement (d) – like lifting a box up a step.
- Power (P) = Work (W) ÷ Time (t) – the rate you do work, similar to how fast a blender spins.
- Energy (E) = Power (P) × Time (t) – total effort over a period.
Concepts with everyday analogies
Newton’s First Law (inertia) says an object at rest stays at rest unless a force acts on it. Picture a coffee mug on a table; it won’t move until you push it.
Newton’s Second Law ties force, mass, and acceleration together. If you try to push a heavy suitcase (large mass) you’ll notice it accelerates slower than a light backpack.
Newton’s Third Law tells us for every action there’s an equal and opposite reaction. When you jump, your legs push down on the ground, and the ground pushes you up.
Ohm’s Law (used in basic circuits) says Voltage (V) = Current (I) × Resistance (R). Think of water flowing through a hose: voltage is the water pressure, current is the flow, and resistance is the hose’s width.
Quick revision table
| Concept | Formula | Everyday Example |
|---|---|---|
| Speed | v = s / t | Car covering 60 km in 1 hour → 60 km/h |
| Force | F = m × a | Pushing a 2‑kg toy with acceleration 3 m/s² → 6 N |
| Work | W = F × d | Lifting a 5‑kg bag 2 m → 5 kg·9.8 m/s²×2 m ≈ 98 J |
| Power | P = W / t | Running up stairs (100 J) in 10 s → 10 W |
| Ohm’s Law | V = I × R | Battery (9 V) through a 3 Ω resistor → I = 3 A |
📝 Likely Exam Questions
- Define inertia and give a real‑life example.
Answer: Inertia is the tendency of an object to keep its state of rest or uniform motion unless acted upon by a force. Example: A ball rolling on a smooth floor keeps moving until friction stops it. - Calculate the force needed to accelerate a 1500 kg car from rest to 20 m/s in 10 seconds.
Answer: Acceleration a = Δv / t = 20 m/s / 10 s = 2 m/s². Force F = m × a = 1500 kg × 2 m/s² = 3000 N. - What is the work done when a 10 kg box is lifted 5 m vertically?
Answer: Work W = m g h = 10 kg × 9.8 m/s² × 5 m = 490 J. - State Ohm’s Law and solve for current when a 12 V battery is connected across a 4 Ω resistor.
Answer: Ohm’s Law: V = I × R. I = V / R = 12 V / 4 Ω = 3 A. - Explain Newton’s third law using the example of a swimmer pushing water backwards.
Answer: The swimmer exerts a backward force on the water; the water exerts an equal forward force on the swimmer, propelling them forward.