Flywheel with weight - Rotational Inertia

[Bryon]

Hey everyone! I have a small problem with part b. I am wondering if i miscalculated something. Any ideas? Thanks!

Homework Statement

A 15 kg flywheel has all its mass around its outer rim. A string is wrapped around it and a m = 4.7 kg weight is hanging on the string. The flywheel has radius R = 0.25 m.


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a) When the 4.7 kg weight is dropping with a speed of 1.1 m/s, what is the angular velocity of the flywheel?
w = rad/s *
4.4 OK


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b) When the 4.7 kg weight is moving with a speed of 1.1 m/s, what is the kinetic energy of the entire system? This one seems really easy, but for some reason I keep getting the wrong answer.

Homework Equations

K(rotational) = 0.5Iw^2
I = 0.5m(wheel)r^2
KE = 0.5m(block)v^2

The Attempt at a Solution

KE(system) = 0.5[0.5m(wheel)r^2]w^2 + 0.5m(block)v^2

0.5*[0.5*15*0.25^2]*(4.4^2) + 0.5*4.7*(1.1^2)
KE(system) = 4.5375 + 2.8435 = 7.381 J


For some reason 7.381 is not correct.

 

[Bryon]

Please?

 

[kerimek]

Hello! It looks like you have used the correct equations and values to calculate the kinetic energy of the system. However, it is possible that you made a calculation error or used the wrong units for the values. I would recommend double checking your calculations and units to ensure accuracy. Additionally, you can try solving the problem using a different method to see if you get the same result. If you are still having trouble, feel free to share your work and we can help you identify any errors. Keep up the good work!