Question

The engine has the flywheel of mass 7 tons and the radius of gyration is 1.7 m. The fluctuation of energy is 55 kN-m. The mean speed of the engine is 150 rpm. What is the coefficient of fluctuation of speed?

(a) 0.021

(b) 0.011

(c) 0.031

(d) 0.041

Answer 1

Right choice is (b) 0.011

Explanation: The fluctuation of energy = ΔE, the mass of the flywheel = m, the radius of gyration = k, the mean speed of the flywheel = N.  ΔE = (frac{π^2}{900})*m*k^2*N*(N1-N2) = (frac{π^2}{900})*7000*1.7^2*150*(N1-N2) = 33277*(N1-N2) ⇒ 55000 = 33277*(N1-N2) ⇒ (N1-N2)=  (frac{55000}{33277}) = 1.652 rpm. Coefficient of fluctuation of speed = Cs = (frac{N_1-N_2}{N}) = (frac{1.652}{150}) = 0.011.