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Question

A wheel has a constant angular acceleration of 5.0 rad/s². Starting from rest, it turns through 300 rad. (a) What is its final angular velocity? (b) How much time elapses while it turns through the 300 radians?

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From  the kinematics of the rotational motion \textbf{ the kinematics of the rotational motion } we know that :

ωf2=ωi2+2α(θfθi)\omega_{f}^2 = \omega_{i}^2 +2\alpha(\theta_{f} - \theta_{i} )

Where:

  • ωf\omega_{f} is the final angular velocity of the body.
  • ωi\omega_{i} is the initial angular velocity of the body.
  • α\alphais the angular acceleration of the body.
  • θi\theta_{i} is the initial angular displacement .
  • θf\theta_{f} is the final angular displacement .
  • tt is the time .

From givens\textbf{givens} we know that : α=5 rad/s2\alpha = 5 \ \mathrm{rad/s^2} , (θfθi)=300(\theta_{f} - \theta_{i}) = 300 rad , ωi=0\omega_{i} = 0 rad/s because the it begins from rest .

plugging\textbf{plugging} known information into the eq. of angular velocity .

ωf2=ωi2+2α(θfθi)ωf=ωi2+2α(θfθi)=0+2×5×300=3000=54.7722\begin{align*} \omega_{f}^2& = \omega_{i}^2 +2\alpha(\theta_{f} - \theta_{i} )\\\\ \omega_{f} &= \sqrt{\omega_{i}^2 + 2 \alpha (\theta_{f} - \theta_{i})}\\\\ &=\sqrt{0 + 2 \times 5 \times 300 }\\\\ &=\sqrt{3000}\\\\ &=54.7722 \end{align*}

ωf=54.7722   rad/s\boxed{\omega_{f} = 54.7722 \ \; \mathrm{rad/s}}

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