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Circular Motion question

2022 · 24 Jun · Shift 2 · Q57
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  5. /2022 · 24 Jun · Shift 2 · Q57

Circular Motion question

2022 · 24 Jun · Shift 2 · Q57

JEE MainPhysicsCircular MotionMCQ+4 / −1
A fly wheel is accelerated uniformly from rest and rotates through 5 rad in the first second. The angle rotated by the fly wheel in the next second, will be :
  1. A
    7.5 rad
  2. B
    15 rad
  3. C
    20 rad
  4. D
    30 rad
View written solutionFree

Correct answer: B

  1. Given

    • The flywheel starts from rest, so initial angular velocity is ω0=0\omega_0 = 0ω0​=0
    • It is accelerated uniformly, so angular acceleration α\alphaα is constant.
    • Angular displacement in the first second is θ1=5 rad\theta_1 = 5\ \text{rad}θ1​=5 rad
  2. Use rotational kinematics For angular displacement in time ttt, θ=ω0t+12αt2\theta = \omega_0 t + \frac{1}{2}\alpha t^2θ=ω0​t+21​αt2

    In the first second, t=1t=1t=1 s: 5=0+12α(1)25 = 0 + \frac{1}{2}\alpha(1)^25=0+21​α(1)2 α2=5\frac{\alpha}{2} = 52α​=5 α=10 rad/s2\alpha = 10\ \text{rad/s}^2α=10 rad/s2

  3. Find total angle in 2 seconds θ(2)=ω0(2)+12α(2)2\theta(2) = \omega_0(2) + \frac{1}{2}\alpha(2)^2θ(2)=ω0​(2)+21​α(2)2 θ(2)=0+12(10)(4)=20 rad\theta(2) = 0 + \frac{1}{2}(10)(4) = 20\ \text{rad}θ(2)=0+21​(10)(4)=20 rad

  4. Angle rotated in the next second This means displacement from t=1t=1t=1 s to t=2t=2t=2 s: θnext second=θ(2)−θ(1)\theta_{\text{next second}} = \theta(2) - \theta(1)θnext second​=θ(2)−θ(1) =20−5=15 rad= 20 - 5 = 15\ \text{rad}=20−5=15 rad

  5. Check options

    • A: 7.57.57.5 rad ❌
    • B: 151515 rad ✅
    • C: 202020 rad ❌
    • D: 303030 rad ❌

Therefore, the correct answer is: 15 rad\boxed{15\ \text{rad}}15 rad​

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