Chapter 10: Problem 1
Do all points on a rigid, rotating object have the same angular velocity? Linear speed? Radial acceleration?
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Chapter 10: Problem 1
Do all points on a rigid, rotating object have the same angular velocity? Linear speed? Radial acceleration?
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Determine the angular speed, in rad/s, of (a) Earth about its axis; (b) the minute hand of a clock; (c) the hour hand of a clock; and (d) an eggbeater turning at 300 rpm.
You're skeptical about a new hybrid car that stores energy in a flywheel. The manufacturer claims the flywheel stores \(12 \mathrm{MJ}\) of energy and can supply \(40 \mathrm{kW}\) of power for 5 minutes. You dig deeper and find that the flywheel is a 39 -cm-diameter ring with mass \(48 \mathrm{kg}\) that rotates at 30,000 rpm. Are the specs correct?
You're asked to check the specifications for a wind turbine. The turbine produces a peak electric power of 1.50 MW while turning at its normal operating speed of 17.0 rpm. The rotational inertia of its rotating structure- three blades, shaft, gears, and electric generator-is \(2.65 \times 10^{7} \mathrm{kg} \cdot \mathrm{m}^{2} .\) Under peak conditions, the wind exerts a torque of \(896 \mathrm{kN} \cdot \mathrm{m}\) on the turbine blades. Starting from rest, the turbine is supposed to take less than 1 min to spin up to its 17 -rpm operating speed. The generator is supposed to be \(96 \%\) efficient at converting the mechanical energy imparted by the wind into electrical energy. During spin-up, the electric generator isn't producing power, and the only torque is due to the wind. Once the turbine reaches operating speed, the generator connects to the electric grid and produces a torque that cancels the wind's torque, so the turbine turns with constant angular speed. Does the turbine meet its specifications?
A solid cylinder and a hollow cylinder of the same mass and radius are rolling along level ground at the same speed. Which has more kinetic energy?
Two forces act on an object, but the net force is zero. Must the net torque be zero? If so, why? If not, give a counterexample.
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