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A person moved from A to B on a circular path as shown in the figure. If the distance travelled by him is 60 m, then the magnitude of displacement would be (Given cos 135° = -0.7)

Asked in JEE Main 25th July 1st Shift 2022 · Distance and average speed

Figure: Distance and average speed
Answer: (2) 47 m

Step-by-step solution

Arc length = rθ with θ = 135° = (3π)/4 rad.

r = (60)/(3π/4) = (80)/π = 25.5 m.

Chord AB by the cosine rule: AB² = r² + r² - 2r² cos 135° = 2r²(1 + 0.7) = 3.4r².

AB = r√3.4 = 25.5×1.84 = 47 m.

Why the other options are wrong

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