#1
So heres the deal. Im not trying to beg UG to do my homework for me but ive been getting my ass kicked by two physics problems. Any advice and or help would be greatly appreciated.

A 600 g steel block rotates on a steel table (μk = 0.6) while attached to a 1.3 m long hollow tube. Compressed air fed through the tube and ejected from a nozzle on the back of the block exerts a thrust force of 4.6 N perpendicular to the tube. The maximum tension the tube can withstand without breaking is 50 N. If the block starts from rest, how many revolutions does it make before the tube breaks?

A conical pendulum is formed by attaching a 410 g ball to a 1.0 m long string, then allowing the mass to move in a horizontal circle of radius 22 cm. The string traces out the surface of a cone, hence the name.
(a) What is the tension in the string?
(b) What is the ball's angular velocity, in rpm?
Quote by karlh07
next thing you know people will be saying anne nicole smith is dead. what a load of crap.


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#3
yes, yes, and you may become may favorite person on UG
Quote by karlh07
next thing you know people will be saying anne nicole smith is dead. what a load of crap.


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#4
I'm having trouble figuring out what goes on in the first one.

In the second one, you've got two forces on the ball: the force of gravity pulling down, and the force of the string pulling up at an angle, which acts as the centripetal force. The ball doesn't move in the z (up-down) direction at all, so we can say

Fz = -mg + T sin theta = 0
mg = T sin theta
(where T is the tension in the string)

We can figure out theta from the length of the string and the radius of the circle
theta = arccos(22 cm / 100 cm)
(theta is the angle between the string and the horizontal)

Then solve the first equation for T and plug in your values
T = mg/sin theta

We know the z component of T is keeping the ball in the air, so the x-y component of T must be keeping the ball moving in a circle.

T cos theta = mv^2/r
v = sqrt(rT cos theta / m)
(sqrt() is the square root function)

v will be a velocity in meters per second, then you convert that to angular frequency (I don't remember how to do that off the top of my head.)

I think that's correct. It's been a while since I've done physics, so forgive me if it's not. Hopefully, that will at least give you someplace to start from.
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#5
Dude
I didn't know UG would do your homework for you
And here I always come on to avoid doing homework
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That never even ever really ends in the end-
Infinity spirals out creation.


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#6
Thanks a ton. Everything was right except you had your sines and cosines backwards. You really saved my butt man, thanks again.
Quote by karlh07
next thing you know people will be saying anne nicole smith is dead. what a load of crap.


Ninth member of the "I watched The cptncacklefanny Soap Opera" club. pm Theplague925 or PapaSmurph to join.