What is the RATE of Rotation help

[8parks11]

What is the RATE of Rotation! help!

An automatic tumble dryer has a 0.65m diamter basket that rotates about a horizontal axis. As the basket turns, the clothes fall away from the basket's edge and tubmle over. IF the colthes fall away from the basket at a point 60 degrees from the vertical, what is the rate of rotation in units of revolutions per minute.


i thought this problem would be extremely simple.

I was wrong :)

First i get

V^2 / rg = tan theta
so i get

Vc^2 = rg tan theta
soif ifind Vc i get 1.785

Now this wouldn't make snese...
does someone else have a different Apporpach

 

[8parks11]

ok i can't get mass from anything. what do i do?

it has tobe something like 0.65 / x = tan theta or something?

 

[ponjavic]

F=mv^2/r

At sixty degrees the vertical part of this centripetal force is provided solely by the weight of the clothes ie mg.

thus mv^2/r*cos60 = mg, am I wrong?

v= sqrt(r*g/cos60) = 2.53m/s? Then remember you have to make it revs/min

cannot see why you are using tan

 

[8parks11]

the answer is 37revs/minute
i did get 2.53m/s and then multiplied it by 60/2pi
wrong wrong :(

 

[ponjavic]

Yeah I get 74 revs/minute =/

I did 2.53/r to get it in rads/sec and then /2pi * 60 = 74...

2 times 37, strange

 

[8parks11]

maybe because the problem gave it in diameters and u used that.
i'm still trying to get it

 

[8parks11]

wait i still don'tget how uget 2.53m/s to 74rev/min

2.53 / (2pi x 60) doesn't work nor (2.53/2pi) x 60

 

[ponjavic]

no i used radius and I told you 2.53/r to get radians per seconds.

2.53/2pi*60 doesn't mean anything. What you want is

2.53/r/2pi*60 to get 74

 

[8parks11]

ok so any idea why it is 74 instead of 37?

 

[ponjavic]

Unfortunately no clue =(

 

[8parks11]

can you give me the exact equation that gives 74.
ive tried so many.. it's so weird.

so 2.53m/s is in seconds so i multiply it by 60 to make it in minutes.
so it turns 2.53x60 m/minutes
now since its in meters i have to divide it by 2pi to make it by revolutions
this gives me 24... Not 74... :(

am i looking for r? what did i do wrong?

 

[ponjavic]

What is 2.53 it is velocity, IE m/s

why would 2.53/2pi give you revs/s? It does not. However 2.53/r gives you rads/s which divided by 2pi gives you revs/s

The exact equation as stated before is!

2.53/r/2pi*60 to get 74

 

[BSCS]

(2.53 x 60) / (2 * pi * .65) = 37.1688006

I think you're forgetting r.

 

[ponjavic]

(2.53 x 60) / (2 * pi * .65) = 37.1688006

I think you're forgetting r.

But r is .65/2 is it not?

 

[BSCS]

"0.65m diamter", you are correct.