Calculating Kinetic Energy of a Rotating Grinding Wheel

[physaru86]

1. A grinding wheel of mass 5 kg and diameter 0.20 m is rotating with an angular speed of 100 rad/s. Calculate its kinetic energy. Through what distance would it have to be dropped in free fall to acquire this kinetic energy? m = 5 kg, r = 0.20/2 m = 0.10 m, g = 10 m/s², ω = 100 rad/s 2. v = r*ω, kinetic energy = (1/2)*m*v²

3. v = (0.10 m)*(100 rad/s) = 10 m/s, kinetic energy = (1/2)*(5 kg)*(10 m/s)² = 250 kgm²/s²..... is this right?

 

[PWiz]

Yes it is. Just calculate the second part, it should be easy for you now.

 

[physaru86]

Yes it is. Just calculate the second part, it should be easy for you now.

what formula to use?

 

[PWiz]

Do you know the formula for gravitational potential energy?

 

[physaru86]

Do you know the formula for gravitational potential energy?

U = m*g*h...?

 

[PWiz]

Correct. Now for what value of $h$ does this expression equal 250 joules?

 

[physaru86]

Correct. Now for what value of $h$ does this expression equal 250 joules?

um... is it a question or are you helping me with the solution..?

 

[PWiz]

um... is it a question or are you helping me with the solution..?

We don't provide direct answers to homework questions here. And I wouldn't be posting in this thread trying to help you if I didn't know the concept myself :)

 

[physaru86]

We don't provide direct answers to homework questions here. And I wouldn't be posting in this thread trying to help you if I didn't know the concept myself :)

Is it related to
Energy conservation during free-fall

 

[PWiz]

Not exactly. It is more to do with energy transformations. The question is simply asking you from which height you'd have to drop this mass for it to have the same kinetic energy when it's about to strike the surface as the value you have calculated (that's what I think the question is asking, since it appears that the question has not been posted verbatim).

 

[physaru86]

Correct. Now for what value of $h$ does this expression equal 250 joules?

m = 5 kg, g = 10 m/s², m*g*h = 250 joules, h = 250/5*10 m, h = 5 m... ?

 

[PWiz]

m = 5 kg, g = 10 m/s², m*g*h = 250 joules, h = 250/5*10 m, h = 5 m... ?

That's right.

 

[physaru86]

That's right.

So the problem is solved, right...? thanks

 

[PWiz]

Your welcome