Turntable question?

Question

A 2.0 kg, 20-cm-diameter turntable rotates at 100 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?

Answer 1

The problem is solved by conservation of angular momentum
angular momentum is I*w

I1*w1=I2*w2
I1=.5*m*r^2
where m=2
r=.2
to convert rpm to rad/sec multiply the rpm by 0.10472
I1*w1=.04*.10472*100
=0.41888

The I2 is
.04+2*.5*.2
=.24

w2=0.41888/.24
=1.74533333
In rpm
=50/3

check
.04*100/.24
=50/3

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