Question

Two wheels of $M.I.3kg{m}^2$ and $5kg{m}^2$ are rotating at the rate of $600rpm$ and $800rpm$ respectively in the same direction. If the two are coupled so as to rotate with the same axis of rotation, the resultant speed of rotation will be (in $rpm$)

• A. $725$
• B. $850$
• C. $420$
• D. $630$

Answer 1

The correct option is A $725$

by conservation of angular momentum

$I\omega =I_1{\omega }_1+I_2{\omega }_2$

$(3+5)\omega =3\times 600+5\times 800=5800$

$\omega =725rpm$