Hw3 Physics PDF

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Hw3 Physics...

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Turn-in Homework #3 Physics 212 Due Tuesday 10/21/2014 1. On a merry-go-round (see photo below) at the playground, Sally Sue and Betty Lou are doing physics! Sally Sue is going for a ride. 45.0 kg Sally Sue stands on the outer edge of a 55.0 kg merry-go-round as her physics buddy Betty Lou pushes it with a constant 48.0 N force, applied tangentially at the outer edge of the merry-go-round. Betty (and the merry-go-round) starts from rest and pushes for 10.0 s, running around circularly so her push is always applied tangentially. At this point Betty quits pushing and the merry-go-round continues to spin at constant angular speed (until Sally moves.) Sally then moves/walks towards the center until she is 1.00 m from the middle of the merry-go-round. The merry-go-round is 6.50 m across and can be assumed to be a flat, solid disk of uniform mass distribution. (Ignore the mass of the bars used for hanging on.) Assume there is negligible friction and that Sally can be approximated as a point particle. a) Show that the work Betty Lou does while pushing is equal to the KE that the merry-go-round and Sally acquire (during that push). b) Find the change in KE of the merry-go-round and Sally from when Sally is at the edge until she is closer to the middle (1.00 m from center).

2. An interesting fire escape possibility involves a platform attached to a rope that is wound around a massive, solid cylindrical flywheel that is free to rotate about its central axis. (See the not-to-scale diagram below.) A person steps out of a window onto the platform and falls at increasing speed to the ground below, causing the flywheel to angularly accelerate at the same time. The massive flywheel constrains the rate at which the person falls to the ground. Assume a safe landing speed to be 2.00 m/s on the ground, 10.0 m below the starting position. Your task is to determine the flywheel mass needed, using three different techniques. The person and platform mass is 80.0 kg; the flywheel’s radius is 0.800 m. a) Solve for mass of flywheel using the law of conservation of energy. b) Solve for mass of flywheel by combining Newton’s 2nd law for translational motion, FNET = ma, for the falling mass and Newton’s 2nd law for rotational motion, τNET = Iα, for the rotating flywheel. c) Solve for mass of flywheel using Newton's 2nd law for rotational motion, τNET = dL/dt for both the flywheel and the falling mass....