# Help me find angular velocity and change in Kinetic Energy

#### samemikejones

got a real tricky but fun problem, wheel A is going 35 rad/s, with I = 25 Kg*m2 and merges into wheel B with I = 15 Kg*m2, if they stick together at contact, find its angular velocity and change in Kinetic Energy...

So far, I have L = IW, or 8.8 x 10^2 kg m2/sec

and L = IW for oval to be at 9.8 x 10^2 kg m2/sec,

w = L/I

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#### OlderDan

Homework Helper
samemikejones said:
got a real tricky but fun problem, wheel A is going 35 rad/s, with I = 25 Kg*m2 and merges into wheel B with I = 15 Kg*m2, if they stick together at contact, find its angular velocity and change in Kinetic Energy...

So far, I have L = IW, or 8.8 x 10^2 kg m2/sec

and L = IW for oval to be at 9.8 x 10^2 kg m2/sec,

w = L/I
Your first computation for the angular momentum looks fine. I have no idea where your second line comes from. The problem is not specific, but I assume they indend for you to assume wheel B starts at rest. The two wheels together have greater moment of inertial than either one separately. Angular momentum must be conserved. How do calculate the kinetic energy?

#### OlderDan

Homework Helper
samemikejones said:
K.E. = 1/2 I omegah squared
OK, so you have an initial $$\omega$$ for each wheel. Use conservation of angular momentum to find their final $$\omega$$ and calculate the initial and final energies.

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