# Tension question (this should be basic)

1. Feb 12, 2006

### nick727kcin

tension question on object moving in a circle (this should be basic)

A .6 kg steel block rotates on a steel table while attached to a 1.20 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 4.10 N perpendicular to the tube. The maximum tension the tube can withstand without breaking is 50.0 N. (coefficient of kinetic friction:.6) If the block starts from rest, how many revolutions does it make before the tube breaks?

im stumped...

look 1 post down... im trying

Last edited: Feb 12, 2006
2. Feb 12, 2006

### nick727kcin

ah i found something:

at= 6.833333 m/s^2

Fr= mat - Ff

Fr= 4.1N- Ff
= 4.1-3.528
=.572N

a(c)= .953333m/s^2

Last edited: Feb 12, 2006
3. Feb 12, 2006

### nick727kcin

ok heres what i tried:

at 50N, the object is going at:
v= 10m/s

so i plugged this in the T=(mv^2)/r equation and got: T=50s, but this looks wrong, and i dont know how to get revs from this...

4. Feb 12, 2006

### nick727kcin

hmmm...

angluar velocity= (at/r)t= 284.722rad/s= 2718.89 rpm

2718.89= 45.315 revs/second

45.315 x 50 = 2265.75 revolutions (wrong)

Last edited: Feb 12, 2006
5. Feb 12, 2006

### nick727kcin

6. Feb 12, 2006

### Tide

Here's a start:

The angular acceleration is given by

$$I \frac {d^2 \theta}{dt^2} = r (F_T - \mu mg)$$

where I is the moment of inertia (essentially just $m R^2$). Use the equation solve for the angular velocity and the angular displacement as a function of time then determine the time at which the centripetal force reaches the breaking point.

7. Feb 12, 2006

### nick727kcin

thank you , thank you for responding

8. Feb 12, 2006

### nick727kcin

thanks so much, but i dont really get what youre saying. what does Ft mean? o, i didnt learn about inertia yet

Last edited: Feb 12, 2006
9. Feb 12, 2006

### nick727kcin

guys, i dont want you to waste your time. if you arent able to help in the next 30 minutes, dont even worry about it