# Hardest question on Physics exam

1. Dec 12, 2011

### bubbaburp

An astronaut on the moon wishes to calculate the local g in the area. He sets up a wire with a mass of 1.7 grams and hanging from it an object with mass 4.98 kg. He sends some kind of pulse down the wire and calculates that it takes 40.86 ms to traverse the wire. What is g. You can neglect the mass of the wire when calculating the tension. That was everything that was given in the problem. I have not a clue how to solve it. What I did was just use the equation of T=2pi[sqrt(l/g)] to solve for g and hope that the wire acts like a spring or something. I'm totally sure that's incorrect, but hey I'm not an astrophysicist.

2. Dec 12, 2011

### Staff: Mentor

Were you given the length of the wire? You'll need it.

You need to figure out the speed of the pulse along the wire. What does it depend on? What physical quantities determine the speed of the pulse?

3. Dec 12, 2011

### bubbaburp

Sorry. Yes, the length was also given. Though I can't remember the value of it anymore. Speed of the pulse I'm guessing is just x/t. X being the length and t being time, right? I don't think we've done problems involving speed of pulse, unless I'm completely unaware of it. A friend of mine told me he used frequency (f) = sqrt(T/μ), where T=tension and μ=mass/length. His way seems correct.

4. Dec 12, 2011