Angular Dynamics

1. Oct 12, 2004

cb

I need help starting this problem. How does that fact that the second wheel starting at rest, effect the problem.

A wheel is rotating freely with an angular speed of 800 rev/min on a shaft whose rotational inertia is negligible. A second wheel, initially at rest and twice the rotational inertia of the first, is suddenly coupled to the same shaft. We have to find (a) the angular speed of the resultant combination of the shaft and the two wheels; (b) the fraction of the original rotational kinetic energy lost in the process.

2. Oct 12, 2004

angular momentum must be conserved. The 2nd wheel adds to the rotational inertia.

3. Oct 12, 2004

cb

Could I say something like this....
$$I_A\omega_A+I_B\omega_B=(I_A+I_B)\omega$$

4. Oct 12, 2004

arildno

No, you must say:
$$(I_{A}+I_{B})\omega_{new}=I_{A}\omega_{old}$$