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Q3.8: NCERT Physics - Part 1 MOTION IN A PLANE 3.8 Solution: Three girls skating on a circular ice ground of radius 200 m…
⚠️ Common Exam Traps & Conceptual Pitfalls
Students often incorrectly calculate displacement as the arc length of the circular path instead of the straight-line chord distance. Remember that displacement is the shortest straight-line distance between initial and final points, which equals the diameter ($2r$) here, not the curved distance traveled.
Three girls skating on a circular ice ground of radius 200 m start from a point P on the edge of the ground and reach a point Q diametrically opposite to P following different paths as shown in Fig. 3.19. What is the magnitude of the displacement vector for each? For which girl is this equal to the actual length of path skated?
Step-by-Step Verified Solution
**Answer:** Displacement magnitude = 400 m for all girls. Equal to path length for the girl who skates along the diameter PQ.
**Step-by-Step Explanation:**
Displacement is the straight-line distance from P to Q. Since P and Q are diametrically opposite, displacement magnitude = 2 _ radius = 400 m for all girls.
The actual path length equals displacement only for the girl who travels along the diameter (straight line PQ). [citation:19]
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