Calculating the Angular Velocity of a Turntable After Blocks Are Dropped on It

[talaroue]

Homework Statement

A 2.05 kg, 33.64 cm diameter turntable rotates at 365 rpm on frictionless bearings. Two 280 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?

Homework Equations

I= m(r^2)/2
Ki=I(w^2)/2

The Attempt at a Solution

I changed the 365 rpm to 38.22 rad/s
Then i found that the Ki=m_t(r^2)(w_i^2)/2
Then i found that the Kf=(m_t+m_b1+m_b2)(r^2)(w_i^2)/2)

Then i solved for w_f and got the equation m_t*w_i^2/(the mass of the turntable and blocks). Then the square root of that and got 33.87 rad/s

Then turned 33.87 rad/s to rpm and got 323.46...Did i use the wrong I maybe? I used the I from above. and combined it with the Kinetic energy.

 

[Doc Al]

You cannot assume that kinetic energy is conserved. But something else is.

 

[talaroue]

momentuem...ahhh i see. stupid mistake on my part.