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RRB JE Motion & Laws

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This page covers RRB JE Motion & Laws with complete concept notes, 12 graded practice MCQs, key points and exam-specific tips. Free to study.

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Concept Notes

Motion & Laws— Rules & Concept

Core ConceptRead this first — the foundation of the topic

Motion and Laws are the backbone of physics. This topic covers how objects move and what forces cause that movement. Newton's three laws of motion form the foundation. CORE CONCEPT:

Motion is the change in position of an object with time. Laws of motion explain why objects start moving, stop moving, or change their speed and direction.

Key RulesCore rules you must know cold

Newton's First Law (Law of Inertia): An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by an external force. Newton's Second Law: Force equals mass times acceleration. F = ma Newton's Third Law: For every action, there is an equal and opposite reaction.

Formula BlockMemorise — at least one formula appears in every paper
F = ma (Force = mass × acceleration)
v = u + at (Final velocity = Initial velocity + acceleration × time)
s = ut + (1/2)at² (Distance = initial velocity × time + half × acceleration × time squared)
v² = u² + 2as (Final velocity squared = Initial velocity squared + 2 × acceleration × distance)
Momentum = mass × velocity
Exam PatternsWhat examiners ask — read before attempting PYQs

RRB Group D frequently asks direct formula applications, especially F = ma problems. Numerical problems on equations of motion are very common. Questions often involve trains, cars, or falling objects. Third law applications like rocket propulsion appear regularly.

ShortcutsUse these to save 30–60 seconds per question
UVAT Method

Remember u, v, a, t, s. Any three given, find remaining two using equations. 2. For free fall problems: Always use g = 10 m/s² for quick calculations instead of 9.8 m/s² 3

Action-Reaction Pairs

Walking, swimming, rocket propulsion - all follow third law

Worked ExampleSolve this step-by-step before moving on

A train accelerates from rest at 2 m/s² for 10 seconds. Find the distance covered. Given: u = 0 m/s (starts from rest), a = 2 m/s², t = 10 s Required: s = ? Solution: Using s = ut + (1/2)at² s = (0)(10) + (1/2)(2)(10)² s = 0 + (1)(100) s = 100 meters WORKED EXAMPLE 2: A 5 kg box is pushed with 20 N force. Calculate acceleration. Given: m = 5 kg, F = 20 N Required: a = ? Solution: Using F = ma 20 = 5 × a a = 20/5 = 4 m/s²

Exam TrapsCommon mistakes students make — avoid these

The #1 trap students fall into is confusing mass and weight. Mass is measured in kg and remains constant everywhere. Weight is force (mg) measured in Newtons and changes with gravity.

Always check if the question asks for mass or weight. Many students write kg when answer should be in Newtons or vice versa. Another frequent error is mixing up action-reaction pairs. The forces act on DIFFERENT objects, not the same object.

When you push a wall, you feel the wall pushing back on you - these are action-reaction forces. For numerical problems, always write given data first, identify what to find, then choose the correct equation. This systematic approach prevents formula confusion and silly mistakes.

Key Points to Remember

  • Newton's First Law: Objects resist change in motion due to inertia
  • Newton's Second Law: F = ma is the most important formula for calculations
  • Newton's Third Law: Action and reaction forces act on different objects
  • Quick formula: v² = u² + 2as for problems without time
  • Free fall shortcut: Use g = 10 m/s² for fast calculations
  • Momentum = mass × velocity, measured in kg⋅m/s
  • UVAT method: Know any 3 of u,v,a,t,s to find other 2
  • Mass is in kg and constant, weight is mg in Newtons
  • Distance formula: s = ut + (1/2)at² for uniform acceleration
  • Acceleration = (final velocity - initial velocity) ÷ time

Exam-Specific Tips

  • Standard gravity g = 9.8 m/s² or approximately 10 m/s²
  • Force is measured in Newtons (N), acceleration in m/s²
  • 1 Newton = 1 kg⋅m/s² (unit of force)
  • Inertia depends only on mass, not on velocity or force
  • Rocket propulsion works on Newton's third law principle
  • Momentum is a vector quantity with direction
  • Uniform motion means zero acceleration
  • Action-reaction forces are always equal in magnitude and opposite in direction
Practice MCQs

Motion & Laws — Practice Questions

12graded MCQs · easy to hard · full solution & trap analysis

All MCQs →
Practice 1easy

A car accelerates uniformly from rest and reaches a velocity of 20 m/s in 5 seconds. What is the acceleration of the car?

Practice 2easy

According to Newton's First Law of Motion, an object will remain at rest or in uniform motion unless acted upon by an external force. What is this property called?

Practice 3easy

A ball is thrown vertically upward with an initial velocity of 30 m/s. Taking g = 10 m/s², what is the maximum height reached by the ball?

Practice 4easy

A force of 50 N is applied to an object with a mass of 10 kg. What is the acceleration produced in the object according to Newton's Second Law?

Practice 5medium

A car accelerates uniformly from rest and reaches a velocity of 20 m/s in 5 seconds. What is its acceleration?

Practice 6medium

According to Newton's second law of motion, force is equal to the product of mass and acceleration. If a 2 kg object experiences a net force of 8 N, what will be its acceleration?

Practice 7medium

An object moves 50 meters in the first 5 seconds and 100 meters in the next 5 seconds. Which statement correctly describes its motion?

Practice 8medium

Which of Newton's laws of motion states that an object at rest remains at rest unless acted upon by an external force?

Practice 9medium

A bus moving at 15 m/s applies brakes and comes to rest in 3 seconds. What is the deceleration of the bus?

Practice 10hard

A car accelerates uniformly from rest and covers 100 m in 5 seconds. What is its acceleration?

Practice 11hard

According to Newton's Second Law of Motion, if the same force is applied to two objects with masses 2 kg and 4 kg respectively, what is the ratio of their accelerations?

Practice 12hard

A ball is thrown vertically upward with an initial velocity of 20 m/s. Taking g = 10 m/s², what is the maximum height reached by the ball?

60-Second Revision — Motion & Laws

  • Remember: F = ma, v = u + at, s = ut + (1/2)at², v² = u² + 2as
  • Formula: Momentum = mass × velocity, Force = Change in momentum ÷ time
  • Trap: Mass is in kg, Weight is in Newtons (mg)
  • Shortcut: Use g = 10 m/s² for quick free fall calculations
  • Key point: Action-reaction forces act on different objects, not same object
  • Method: UVAT technique - identify given values first, then choose equation
  • Common error: Don't confuse distance (s) with displacement in problems
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