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Unformatted text preview: homework 10 – ALIBHAI, ZAHID 1 Latest unpenalized work: Apr 2 2007 Monday 04:00 (after this date you can not make a perfect score). Work cutoff: Apr 4 2007, 4:00 am. Question 1 part 1 of 1 10 points A flywheel of radius 0 . 53 m and moment of inertia of 17 . 5 kg · m 2 rotates initially at a rate of 7 . 3 revolutions / sec. If a force of 3 . 1 N is applied tangentially to the flywheel to slow it down, how much work will be done by this force in bringing the flywheel to a stop? 1. 1 . 643 J 2. 18408 . 3 J 3. 127 . 75 J 4. 466 . 287 J 5. 932 . 575 J 6. 36816 . 6 J 7. 802 . 677 J Question 2 part 1 of 2 10 points A car is designed to get its energy from a rotating flywheel with a radius of 1 . 75 m and a mass of 571 . 5 kg. Before a trip, the disk-shaped flywheel is attached to an electric motor, which brings the flywheel’s rotational speed up to 1721 . 0 rev / min. a) Find the kinetic energy stored in the flywheel. Answer in units of J. Question 3 part 2 of 2 10 points b) If the flywheel is to supply as much energy to the car as a 7311 W motor would, find the length of time the car can run before the flywheel has to be brought back up to speed again. Answer in units of s. Question 4 part 1 of 1 10 points Given: A circular shaped object with an inner radius of 8 . 3 cm and an outer radius of 21 cm. There are three forces (acting perpen- dicular to the axis of rotation) whose magni- tudes are 12 N, 26 N, and 15 N acting on the object, as shown in the figure. The force of magnitude 26 N is 33 ◦ below horizontal. 12 N 15 N 26 N 11 kg 33 ◦ ω 8 . 3 cm 21 cm Find the magnitude of the net torque on the wheel about the axle through the center of the object. Answer in units of N m. Question 5 part 1 of 1 10 points Given: g = 9 . 8 m / s 2 , I = 1 . 09 kg m 2 , R = 0 . 277 m , k = 71 . 7 N / m , m = 0 . 404 kg , d = 0 . 11 m , and θ = 44 . 7 ◦ . The pulley shown has a radius R and mo- ment of inertia I . One end of the mass m is connected to a spring of force constant k , and the other end is fastened to a cord wrapped around the pulley. Assume: The pulley axle and the incline are frictionless. homework 10 – ALIBHAI, ZAHID 2 R m k θ If the pulley is wound counterclockwise so as to stretch the spring a distance d from its equi- librium position and then released from rest, find the angular speed of the pulley when the spring is again unstretched ( i.e. , at the spring’s equilibrium position). Answer in units of rad / s. Question 6 part 1 of 1 10 points A uniform horizontal rod of mass 1 . 3 kg and length 0 . 68 m is free to pivot about one end as shown. The moment of inertia of the rod about an axis perpendicular to the rod and through the center of mass is given by I = m ℓ 2 12 ....
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