Mass ~ can someone check my answer real quick?

[twenty5]

Homework Statement

I have a pendulum sitting at 15 degrees from the vertical, it does 1 revolution every 2 seconds. the chain is 1.0m long. The tension is 2.0N


My question is which Method would be correct? My professor said, that Method I is the same a Method II (the ones I wrote on the solution) except, the resulting mass does not equal each other. He also told us, use what you can do get the answer quick or something... this was the reply when I asked that the second method incorporates centripetal force,velocity, and the radius... while the first one does not?

thank you so much guys, I really need an answer before I present this to him :S I have an exam tomorrow unfortunately.

Homework Equations

Fy = 0 ; -Fg + Ftcos15 = 0
Fx = Ftsin15 = (mv^2)/2

The Attempt at a Solution

provided..
[PLAIN]http://img560.imageshack.us/img560/9695/questionm.jpg

 

[zhaos]

I'm not sure. Are all the data given compatible? Given all the data available to you, both methods seem to be ok.

 

[twenty5]

they both seem to be okay... but the masses are different! I don't want to get this wrong on the test :S

we're solving for the mass. Everything on the diagram is what was given and calculated

 

[iRaid]

I think your step 2 is wrong... Why are you using diameter for the distance in v=d/t?

(On another note, I know some teachers don't like when you put a 0 with a line through it. For example, my teacher says you only use that for an empty set, although I'm not sure if your teachers care.)

 

[twenty5]

I think your step 2 is wrong... Why are you using diameter for the distance in v=d/t?

(On another note, I know some teachers don't like when you put a 0 with a line through it. For example, my teacher says you only use that for an empty set, although I'm not sure if your teachers care.)

sorry d = distance, I should have put s instead xD

I also put C = 2(pi)r ... = d ... therefore d = C

and naww, I don't think any of my profs care haha.. it's a habit of mine :)