First slide

Rotational motion

Question

A flywheel rotating about a fixed axis has a kinetic energy of 360 J when its angular speed is 30 rad s^-1. The moment of inertia of the wheel about the axis of rotation is

Moderate

A

0.6 kg m^-2
B

0.15 kg m^-2
C

0.8 kg m^-2
D

0.75 kg m^-2

Solution

Rotational kinetic energy $= \frac{1}{2} {Iω}^{2}$
$\begin{array}{l} 360 = \frac{1}{2} I \times 30 \times 30 \\ I = \frac{360 \times 2}{30 \times 30} {kgm}^{2} = 0 .8 {kgm}^{- 2} \end{array}$

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