# Rotational energy levels

1. May 26, 2012

### leopold123

Hello forum members...
I have a problem in calculating the energy of rotational levels. Kindly help me....The question goes like this:

A Caroussel(merry-go-round) of diameter 20 m and weight 1 ton( =1000 kg that is evenly distributed on the discs) rotates 10 times per minute. Calculate the energy of rotational levels and the angular moment quantum number.

Well, the energy of rotational levels is given as:

E=BJ(J+1); B is the rotational constant which is given as, B=h^2/8π^2Iand J=0,1,2....

Since i know the mass of the object and the diameter, i could calculate the moment of inertia I using I=mr^2, r is the radius. so my I= 100000kg/m^2

I dont know what to do now. How should i proceed further to calculate the energy of rotational levels?....Please help me.... Thanks...:)

2. May 26, 2012

### Staff: Mentor

Forget about "rotational levels" for a moment.

What is the energy of the merry-go-round in terms of classical physics?

3. May 26, 2012

### leopold123

i assume that would be the kinetic energy, K.E= L^2/2I

4. May 26, 2012

### Staff: Mentor

Good. Can you calculate J for that value?

5. May 27, 2012

### leopold123

I am sorry...I cant....could you show me, please?

6. May 27, 2012

### leopold123

Could you please show me how can one calculate the j values????...please

7. May 27, 2012

### Staff: Mentor

Just plug everything into the given equation and solve for J, there is no magic in there, just a simple high school algebra. You are expecting something difficult and it blinds you.

8. May 27, 2012

### leopold123

ok...does this mean that I am supposed to find out K.E using K.E=L^2/2I and plug this value in E=BJ(J+1)????...I can find out B because i know inertia...so i have B, I and if i find K.E, i ll get J....thats what you mean, dont you???

9. May 27, 2012

### Staff: Mentor

Yes, this is a simple plug and chug.