物理習題(原文)-高手請進!

(1) A grindstone of radius 10 cm and moment of inertia 0.2 kg-m^ rotates at 200 rpm. A tool is pressed against the rim with force of 50N along radial direction. The coefficient of kinetic friction is 0.6. (a) What is the power needed to keep the stone rotating at a fixed rate? (b) If the drive is removed

how long would it take for the stone to stop? (c) How many revolution does it take while slowing down?(2) A fiywheel initially rotating at 1200 rpm stops in 4 min when only friction acts. If an additional torque of 300N-m is applied

it stops in 1 min. (a) what is the moment of inertia of the wheel? (b) What is the frictional torqe? 麻煩請解題的高手們

列出算式...謝謝!因英文不好...怕翻譯翻錯

所以打原文...謝謝!
(1)r = 10 cm = 0.1 mI = 0.2 kg-m2n = 200rpm