qz6sol_3705sp10 - angular acceleration of the disk is ω 2...

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TA: Tomoyuki Nakayama Monday, March 1 st , 2010 PHY 2048: Physic 1, Discussion Section 3705 Quiz 6 (Homework Set # 8) Name: UFID: Formula sheets are not allowed. Calculators are allowed. Do not store equations in your calculator. You need to show all of your work for full credit. ________________________________________________________________________________ A disk rotates about its central axis starting from rest and accelerates with constant angular acceleration. At one time it is rotating at 20.0 rev/s; 80 revolutions later, its angular speed is 25 rev/s. a) What is the angular acceleration? We use the kinematics equation which relates angular velocity with angular displacement. The
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Unformatted text preview: angular acceleration of the disk is ω 2 2 – ω 1 2 = 2αΔθ α = (ω ⇒ 2 2 – ω 1 2 )/(2Δθ) = 1.41 rev/s 2 (= 8.85 rad/s 2 ) b) What is the time required to complete the 80 revolutions? Using the kinematics equation for angular velocity, we get ω 2 = ω 1 + αΔt Δt = (ω ⇒ 2- ω 1 )/α = 3.55 s c) What is the number of revolutions from rest until the time the disk reaches the 25 rev/s angular speed? Like part a), we use the kinematics equation which relates angular velocity with angular displacement. This time we know the angular acceleration but the angular displacement is unknown. ω 2 2 – 0 2 = 2αθ θ = ω ⇒ 2 2 /2α = 222 rev...
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