# Homework Help: Tension and circular motion

1. Mar 20, 2005

### bpb85

A 500g steel block rotates on a steel table while attached to a 1.2m long hollow tube. Compressed air fed through the tube and ejected from the nozzle on the back of the block exerts a thrust force of 4.0N perpendicular to the tube. The maximum tension the tube can withstand without breaking is 50N. If the block starts from rest, how many revolutions does it make before the tube breaks?

This is a problem from the back of the book that I already know the answer to (3.75) but I think my way of getting it is wrong since I can't get the right answer to a similar problem with different numbers.

What I did first is divide the thrust by the weight 4N/.5kg= 8m/s^2, then I set the tension of 50N equal to the acceleration times the distance times kinetic friction

50N = 8m/s^2*distance*.6

this gets me the right answer of 3.75 revolutions but when the numbers are changed to 4.1N thrust and 60N max tension the answer I come up with (4.39) is wrong.

Anyone have any ideas?

2. Mar 20, 2005

### bpb85

actually looking back, it's 50N= 8m/s^2*distance, so you get 6.25, then multiply that by .6

6.25*.6=3.75 revolutions.

Last edited: Mar 20, 2005