# Angular Momentum/Impulse Problem

by cdbowman42
Tags: angular momentum
 P: 14 [b]1. A 1.8 kg, 20 cm diameter turntable rotates at 160 rpm on frictionless bearings. Two 500 g blocks fall from above, hit the turntable simultaneously at opposite ends of a diagonal, and stick. What is the turntable's angular velocity, in rpm, just after this event? [b]2. Angular momentum(L)=angular velocity(w)*moment of inertia(I) [b]3. I'm confused as to whether or not to appraoch this as a conservation of momentum problem or some other way. I think I would need to know the velocities of the blocks before they hit to to this.
 P: 844 Do the blocks carry with them any angular momentum of their own? (It seems the problem is set up to hint that they do not).
 P: 14 Thanks! thats all I needed!
HW Helper
Thanks
P: 26,148
Angular Momentum/Impulse Problem

hi cdbowman42!
 Quote by cdbowman42 I think I would need to know the velocities of the blocks before they hit to to this.
hint: what was their angular momentum about the axis, before they hit?

(assuming they fell vertically at speed v)
 P: 283 I would think about it in the following way $$\int \tau dt = \Delta ( I \omega)$$ where $$\int \tau dt$$ is the angular impulse and $$\Delta (I \omega)$$ is the change in angular momentum. We can see that no vertical torque is exerted on the turntable, so the angular momentum must remain constant. Then we must have $$(I \omega)_{initial} = (I \omega)_{final}$$

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