The radius of wheels of a car moving with a speed of 72kmh−1 is 0.25m. If by applying brakes the wheels are stopped in 20 rotations, then the angular retardation produced by the brakes is
A
−25.5rads−2
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B
−20.5rads−2
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C
−29.5rads−2
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D
−33.0rads−2
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Solution
The correct option is A−25.5rads−2 By using the equation ω2=ω20+2αθ angular retardation, α=ω2−ω202θ....(i) We know that, ω0=vr=72×5/180.25 =80rads−1....(ii) When, ω=0,θ=2πn i.e., θ=2π×20=40πrad....(iii) Substituting, values of Eqs. (ii) and (iii) in Eq. (i), we get α=02−(80)22×40π=−80×8080×3.14=−25.5rads−2.