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Unformatted text preview: Physics 130 Exam 4 Short Answer section. Please answer all of the short answer questions. 1. A disk rotates with an angular velocity ω of 10 rad/s. If the disk has a mass of 50 kg and has a radius of 1.5m, what angular momentum and kinetic energy does this disk have? What is the linear velocity of the edge of the disk? I disk = 1 2 m r 2 I disk = 1 2 mr 2 = 1 2 ⋅ 50 kg ⋅ (1.5 m ) 2 = 56.25 kgm 2 L = I disk ω = 56.25 kgm 2 ⋅ 10 rad / s = 562.5 kgm 2 / s KE = 1 2 I disk ω 2 = 1 2 ⋅ 56.25 kgm 2 ⋅ (10 rad / s ) 2 = 2812.5 J v = r ω = 1.5 m ⋅ 10 rad / s = 15 m / s 2. A force of 200 N is applied to a sphere of mass 150 kg and radius 1 m as shown below. What torque and angular acceleration does this sphere experience? I sphere = 2 5 mr 2 (Angle is in degrees with respect to a radial line) 30 τ = r F sin θ = 1 m ⋅ 200 N ⋅ sin 30 = 100 Nm I sphere = 2 5 mr 2 = 2 5 ⋅ 150 kg ⋅ (1 m ) 2 = 60 kgm 2 τ = I α α = τ I = 100 Nm 60 kgm 2 = 1.67 rad / s 2 3. A sphere experiences a constant angular acceleration of 10 rad/s 2 for 20s. If the sphere spins up from rest, what Fnal angular velocity and through what angle does the sphere turn? ω f = ω i + α t = + 10 rad / s 2 ⋅ 20 s = 200 rad / s θ f = θ i + ω i t + 1 2 α t 2 = + + 1 2 ⋅ 10 rad / s 2 ⋅ (20 s ) 2 = 2000 rad 4. A solid sphere (mass m and radius r,...
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 Spring '10
 jojo
 Force, Mass, Velocity, Sin, Orders of magnitude

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