The flywheel of a gasoline engine is required to give up 510 J of kinetic energy
ID: 1460758 • Letter: T
Question
The flywheel of a gasoline engine is required to give up 510 J of kinetic energy while its angular velocity decreases from 700 revolutions per minute to 540 revolutions per minute. What is the required moment of inertia?
My approach has been as follows: I define kinetic energy as (1/2) I w^2 , then set this equal to 570 joules. I use the final angular velocity (given) and solve for Inertial moment. However, that gives me a huge number that is not correct.
Could someone help guide me toward the right answer please? Thanks for your time and assistance.
Explanation / Answer
Rotational kinetic energy = 1/2Iw^2
rpm in rad/sec
700 rpm = 73.3 rad/sec
540 rpm = 56.54 rad/sec
KE = 0.5*I*(w1^2 - w2^2) = 570 J
1140 = I*(73.3^2 - 56.54^2)
I = 1140/(73.3^2 - 56.54^2) = 0.523 kg.m^2