A flywheel for energy storage in a hybrid gasoline-electric car is a ring-shaped rotor of mass 50 kg, designed to rotate at 30000 rpm. At that speed it stores 10 MJ of energy (equivalent to about a cup of gasoline). What is the ring's diameter?
n=30000 rpm=30000/60=500rev/s,
ω=2πn=2•3.14•500= ...
ME=10•10⁶ J =10⁷J
KE=Iω²/2 =mR²ω²/2
R=sqrt(2•KE/m• ω²)=…
D=2R