NCERT Solutions Class 11 Physics Chapter 2 Motion in a Straight Line

The Class 11 Physics NCERT Solutions Chapter 2 Motion in a Straight Line will help students prepare for Boards, JEE Main, JEE Advanced, NEET, CUET and NDA in 2026-27. Every back-exercise question is solved with full working, so students can follow each graph reading, velocity calculation, and kinematic-equation step one line at a time.

This chapter builds the base of kinematics that Chapter 3 Motion in a Plane then extends to two dimensions.

• CBSE Weightage: 5 to 7 marks, usually one short answer on graphs plus one numerical on the kinematic equations.
• Questions solved: all Exercise 2.1 onward, covering displacement, velocity, acceleration, motion graphs, and relative velocity.
• Key formulas: the three equations of uniformly accelerated motion, average velocity, and relative velocity in one dimension.

Each solution in this Class 11 Physics NCERT Solutions Chapter 2 Motion in a Straight Line compilation is curated by subject experts, based on the 2026-27 NCERT textbook, and refined against the last five years of CBSE Board, JEE Main and NEET papers.

Distance, Displacement and Path Length in Straight-Line Motion

Kinematics starts by fixing what we mean by "how far" an object has moved. The chapter draws a sharp line between path length (the total ground covered) and displacement (the straight change in position). Getting this pair right is the first step in almost every numerical here.

The NCERT questions here ask students to compare these two quantities for a moving object. Displacement can be zero even when the path length is large, such as when an object returns to its start. The solved answers show the sign of displacement on its own line, so students never confuse the two. This single habit fixes the most common error in the opening exercises.

Average Velocity and Average Speed in the Motion Chapter

Once position is defined, the chapter measures how fast it changes. Average velocity uses displacement, while average speed uses path length. The two are equal only when the motion never reverses direction, and the NCERT solutions test that idea directly.

• Average velocity: displacement divided by the time taken, v̄ = Δx/Δt. It is a vector and carries a sign.
• Average speed: total path length divided by total time. It is a scalar and is never negative.
• When they match: for motion in one direction with no turning back, average speed equals the size of average velocity.

Numericals such as Exercise 2.1 give a trip with a return leg and ask for both quantities. Read the direction of each leg before you add anything, because displacement can cancel while path length keeps growing. The step-by-step answers set out each leg separately, so the sign work is easy to follow.

Instantaneous Velocity and Instantaneous Speed

Instantaneous velocity is the velocity at a single moment, found as the limit of average velocity over a shrinking time interval. On a position-time graph it is the slope of the tangent at that instant. The chapter uses this idea to move from average to point-by-point motion.

Questions here ask students to find velocity at a given instant from a position-time equation or graph. Instantaneous speed is just the magnitude of instantaneous velocity, so the two always have the same numerical value at a point. The solutions differentiate the position equation step by step, then substitute the time, so no stage is skipped.

Acceleration: Uniform and Non-Uniform Motion

Acceleration is the rate at which velocity changes with time. When it stays constant the motion is uniformly accelerated, and when it varies the motion is non-uniform. The NCERT solutions handle both, and most board numericals sit in the uniform case.

• Average acceleration: change in velocity divided by time taken, ā = Δv/Δt.
• Instantaneous acceleration: the limit of average acceleration, a = dv/dt, equal to the slope of the velocity-time graph.
• Sign of acceleration: negative acceleration slows an object only when velocity is positive; it can also speed up an object moving the other way.

Exercises like Exercise 2.4 ask students to read acceleration from a velocity-time graph. Acceleration is the slope of the velocity-time graph, not the value of the velocity itself. Mixing these two up is a frequent slip, so the solved answers mark the slope and the value in separate steps.

Kinematic Equations for Uniformly Accelerated Motion

The heart of the chapter is the three equations of motion for constant acceleration. Every board numerical on straight-line motion uses one of them. The Class 11 Physics NCERT Solutions Chapter 2 Motion in a Straight Line apply these equations with each substitution shown, so students can reproduce the working in the exam.

Numericals such as Exercise 2.6 give three of the five quantities and ask for a fourth. Pick the equation that already contains the three known values, so you solve for the unknown in one step. These equations work only when acceleration is constant, and the solutions state that condition before using them, including for free fall where a = g.

Position-Time and Velocity-Time Graphs

Graphs are the visual half of this chapter, and CBSE loves to test them. A position-time graph shows where an object is at each moment, while a velocity-time graph shows how fast it moves. Reading slopes and areas off these graphs answers many one-mark and two-mark questions.

• Slope of a position-time graph gives velocity; a straight slanted line means constant velocity.
• Slope of a velocity-time graph gives acceleration; a horizontal line means zero acceleration.
• Area under a velocity-time graph gives displacement over that time interval.

Questions like Exercise 2.5 ask students to describe motion from a graph or to sketch one. The area under the velocity-time graph is the displacement, so add areas above the time axis and subtract those below it. The Class 11 Physics NCERT Solutions Chapter 2 Motion in a Straight Line shade the area and label its sign, which makes the graph questions quick to score.

Relative Velocity in One Dimension

The last major idea is relative velocity: how fast one object moves as seen from another. In one dimension it is just a subtraction with signs, and the chapter uses it for problems on two trains, two cars, or a boat in a stream along a line.

Numericals here give the speeds of two bodies and ask when they meet or how far apart they are. Relative velocity of A with respect to B is v_A − v_B, so choose one direction as positive before you substitute. The solutions fix the positive direction first and keep it through every line, which is exactly how NCERT expects the relative-motion answers to read.

Exercise-wise Breakdown for Class 11 Physics Chapter 2 Motion in a Straight Line

The NCERT back-exercise splits into clear groups. Use this map to plan which answers to practise first for the 2026-27 boards. Every group links to the full solved set.

Solving the groups in this order builds the skills in the same sequence the chapter teaches them. Start with displacement, then graphs, then the equations of motion, because each group uses the one before it.

Common Mistakes Students Make in the Motion in a Straight Line Chapter

These slips happen while reading a graph or substituting into a formula, not because the concept is unclear. Each one costs 1 to 3 marks in the CBSE paper, so the solved answers point them out at the exact step.

Student Feedback on the Motion in a Straight Line Chapter

Practice Questions for Class 11 Physics Chapter 2 Motion in a Straight Line

Once the solved answers are clear, test yourself on the full question set. The practice page has every NCERT question with a step-by-step Solution and an Expert Solution behind a click.

Other Motion in a Straight Line Class 11 Physics Resources

NCERT Solutions for Class 11 Physics: All Chapters

Jump to the solutions for any other Class 11 Physics chapter below.

FAQs on Class 11 Physics Chapter 2 Motion in a Straight Line NCERT Solutions