A light rod of length ℓ = 1.00 m rotates about an axis perpendicular to its leng

Physics
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A light rod of length ℓ = 1.00 m rotates about an axis perpendicular to its length and passing through its center as in the figure below. Two particles of masses m1 = 4.45 kg and m2 = 3.00 kg are connected to the ends of the rod.

(a) Neglecting the mass of the rod, what is the system's kinetic energy when its angular speed is 2.20 rad/s?
  
The correct answer is not zero. J

(b) Repeat the problem, assuming the mass of the rod is taken to be 2.30 kg.
  
Jun 11th, 2015

Thank you for the opportunity to help you with your question!

 (a) the kinetic energy is given by the sum of the rotational kinetic energies for each of the masses. 
KE = (1/2)Ia*w^2 + (1/2)Ib*w^2 
KE = (1/2)w^2[Ia + Ib] 

For point masses the moments of inertia are: 
Ia = ma*R^2 
Ib = mb*R^2 

KE = (1/2)w^2R^2[ma + mb] 

w = 2.5 
R = 1/2 
ma = 4 and mb = 3 

KE = (1/2)(2.2)^2(1/2)^2[4.45 + 3] 
KE = 4.51

(b) The KE of the masses will be the same so we only need calculate the kinetic energy contribution from the rod. 

KErod = (1/2)Ir*w^2 
Ir = (1/12)mL^2 = (1/12)2.3(1^2) = 0.191
KErod = (1/2)0.191(2.2^2) = 0.462




Please let me know if you need any clarification. I'm always happy to answer your questions.
Jun 11th, 2015

are sure because i get one chance to try

Jun 11th, 2015

I have pressure now, what if it's not right... you may want to post it again so another tutor can do it?

Jun 11th, 2015

you did the Q to my brother correct and me not why ????    -_-

Jun 11th, 2015

oh I didn't know~~sorry. Yeah go ahead and put the answers in

Jun 11th, 2015

no the number are not the same but thank i am sad and i don't need your help maaslamih 

Jun 11th, 2015

the answers are wrong?

Jun 11th, 2015

i do not know 


Jun 11th, 2015

can you go back and chick my brother answer or the problem and make sure 

Jun 11th, 2015

the question still have the same number right? Let him invite me to the question again, I can't find it

Jun 11th, 2015

ok some of the number are different  

Jun 11th, 2015

i did 


Jun 11th, 2015

just post the question again since the numbers are different..

Jun 11th, 2015

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