1. A small fly wheel fitted to a motor with a moment of inertia of 80 kg m² slows down from 9000 rpm to 5500 rpm in 7.5 seconds.
For the fly wheel, calculate:
• The rate of deceleration which you can assume to be constant
• The braking torque.
2.If the energy used to heat up a block of 2kg of copper is 115.8 kJ, what is the temperature it was heated to if the starting temperature was 100oC and the specific heat capacity is 386 J/kgK.
Answer This Question
a. wf=wi+alpha*t
5500*2PI= 9000*2PI+alpha*7.5
angular acceleratin=-(3500*2PI)/7.5 rad/sec^2
b. Torque:
wf^2=wi^2+2*torque*displacement
where displacement=avg speed*time
= (9000+5500)*PI * 7.5 radians
solve for torque