Question 2
A farmer moves along the boundary of a square field of side 10 m in 40 s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds from his initial position?

Given,
Time period of travel = 2 minutes 20 seconds
Convert min into sec
1 min = 60 sec
So 2 min 20 sec = (2 x 60) sec + 20 sec = 120 + 20 = 140 sec
Side of the given square field = 10 m
Hence, the perimeter of a square = 4 x side = 4 x 10 = 40 m
Time taken by the farmer to cover the boundary of 40 m = 40 s
So, in 1 s, the farmer covers a distance of = x 1 = 1 m
Hence, distance covered by the farmer in 140 sec = 140 m
The total number of rotations taken by the farmer to cover a distance of 140 m
=
=
= 3.5
If the farmer starts from point A, after 3.5 rounds he will be at point C of the field.
∴ Displacement (from Pythagoras theorem)
Hence, the magnitude of displacement = 14.14 m
Chapter 7: Motion — Quick Reference
Quick Revision Points
- Distance (scalar, total path) vs Displacement (vector, shortest path)
- Speed = distance/time (scalar); Velocity = displacement/time (vector)
- Acceleration a = (v−u)/t; unit: m/s²
- Equations: v = u + at; s = ut + ½at²; v² = u² + 2as
- d-t graph slope = speed; v-t graph slope = acceleration; area under v-t = distance
- 1 km/h = 5/18 m/s; Free fall: u = 0, a = g = 9.8 m/s²
- Uniform circular motion: constant speed, changing velocity (direction changes)
- Read the detailed chapter notes for complete coverage of all NCERT topics.
- Practice all NCERT in-text and back exercise questions — they are frequently asked in exams.
- Focus on comparison tables, diagrams, and definitions — these are high-scoring areas.
- For numericals (if applicable), practice at least 20 problems of varying difficulty.
- Refer to the practice question bank (200+ questions) for thorough preparation.
- Detailed Notes: ch07-motion.html
- Practice Questions: 100+ questions with answers in 05-practice-questions/
- Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
- Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html