A fly wheel is a uniform disc of mass 72 kg and radiu 50 cm. When it is rotating at the rate of 70 rpm, its kinetic energy is

Options

A. 142 J
B. 242 J
C. 342 J
D. 300 J

Answer

B

Explanation

Kinetic energy of flywheel , `K = (1)/(2) I omega^(2) = (1)/(2) xx (1)/(2) MR^(2) omega^(2) = (1)/(4) MR^(2) omega^(2)`
=`(1)/(4) xx 72 ((50)/(100))^(2) ((2pi xx 70)/(60))^(2) = 241.5 J - 242 J`.