# Masses hanging from ceilings by strings

1. Aug 1, 2010

### gedanken6

1. The problem statement, all variables and given/known data
A body of large mass is suspended by means of a string A from the ceiling, and another similar string B is attached to the bottom of the body. Which string would break when string B is pulled (a) sharply, and (b) steadily? Why?

2. Relevant equations
F=ma

3. The attempt at a solution
I assume string B would break first. I'm not sure why. On string A, I've labelled T with an arrow going one way, and one going the opposite way on the string. This seems vaguely familiar to me. I've drawn an arrow from the large down labelled g. Unfortunately, I'm not very good at this sort of thing, but I want to become a pro.

2. Aug 1, 2010

### Ken Roberts

Well, this is not going to be helpful with the problem as a homework assignment, but it was interesting.

Using a 2-pound hammer, and two fish scales (range 0-8 pounds) with a stout cord, gives these results. Let A,B denote the forces in their respective strings. When B=0 (no pull on string B), A = 2. If B=4, then A=6. If B=6, then A=8. So that suggests string A would break first. Did not test to breakage point - might have damaged the fish scales.

On the other hand, using the same setup but with a thin string not a stout cord, string B broke first whether additional force was applied gradually or suddenly. Only one trial was made for each speed of force application. Possibly related to non-uniformity in the two thin strings, though they were from the same spool.

Anyway, a nice little "you can do this at home" experiment. Suggests trying other configs, not just linear, making these problems more than textbook paper exercises. Thanks!

3. Aug 1, 2010

### thrill3rnit3

Have you tried impulse?