Question

A flywheel of mass 20 kg and radius 5 cm is revolving at a speed of 300 rpm. Its kinetic energy is ______.

Options

• `25/pi` J

• 2.5`pi^2` J

• 3.6`pi^2` J

• 1.6 `pi^2` J

Answer 1

A flywheel of mass 20 kg and radius 5 cm is revolving at a speed of 300 rpm. Its kinetic energy is  2.5 `pi^2` J. 

Explanation:

M = 20kg

R = 5 cm= 0.05 m

n = 300 rpm=`300/60` = 5 rps

∴ I= MR² = (20) x (0.05)² = 0.05 kg m²

∴ E = `1/2 "I"omega^2`

= `1/2 "I" (2pi"n")^2`

= `2pi^2  "In"^2`

= `2pi^2 xx (0.05) xx 25 = 2.5pi^2 ` J