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# lecture22 - 1 Physics 1D03 Energy Serway 8.1 – 8.3 •...

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Unformatted text preview: 1 Physics 1D03 Energy Serway 8.1 – 8.3 • Rotational work and kinetic energy • Work and potential energy Practice problems: Chapter 10, problems 21, 43, 49, 50. Physics 1D03 Rotational Work A bit of work, dW , is done in turning a nut through a tiny angle d θ : θ τ θ φ φ d d r F ds F dW ) sin ( ) sin ( = = = ⋅ = ds F φ r F ds = rd θ d θ θ τ d dW = θ τ Δ = W So, and for a constant torque, 2 Physics 1D03 Power: dt d dt d dt dW P θ τ θ τ = = = ) ( (angular velocity must be expressed in radians/second). ω τ = P So, Physics 1D03 Quiz A power screwdriver is intended to provide a torque of 0.5 N·m while turning at 120 revolutions per minute. The minimum power needed from the motor will be about A) 60W B) 6 W C) 1 W 3 Physics 1D03 Kinetic energy of a rotating rigid body: Add up the kinetic energies of the particles: 2 2 1 i i i i i v m K K ∑ ∑ = = ω i i r v = but 2 2 1 2 2 2 1 ω ω I r m K i i i = = ∑ so θ v i ω K = ½ I ω 2 (pure rotation)...
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lecture22 - 1 Physics 1D03 Energy Serway 8.1 – 8.3 •...

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