Question

A wheel of moment of inertia $2Kg{m}^2$ is rotating about an axis passing through centre and perpendicular to its plane at a speed $60rad/s$. Due to friction, it comes to rest in $5$ minutes. The angular momentum of the wheel three minutes before it stops rotating is

• A. $24Kg{m}^2/s$
• B. $48Kg{m}^2/s$
• C. $72Kg{m}^2/s$
• D. $96Kg{m}^2/s$

Answer 1

The correct option is C $72Kg{m}^2/s$

$w_f=w+\alpha t\to 0=60+\alpha \times 300$

$\alpha =\frac{-1}{5}$

now to calculater $w$ after 2 min

$w_2=60-\frac{1}{5}120=36$

$L=Iw=2\times 36=72Kg{m}^2/s$