
#1
Apr2111, 04:18 PM

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. 



#2
Apr2111, 04:21 PM

P: 498

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).




#3
Apr2111, 04:22 PM

P: 14

Thanks! thats all I needed!




#4
Apr2111, 04:23 PM

Sci Advisor
HW Helper
Thanks
P: 26,167

Angular Momentum/Impulse Problem
hi cdbowman42!
(assuming they fell vertically at speed v) 



#5
Apr2111, 05:04 PM

P: 284

I would think about it in the following way
[tex] \int \tau dt = \Delta ( I \omega) [/tex] where [tex] \int \tau dt [/tex] is the angular impulse and [tex] \Delta (I \omega) [/tex] 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 [tex] (I \omega)_{initial} = (I \omega)_{final} [/tex] 


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