# Simple physics math help

1. Oct 18, 2007

### klm

What is the tension in the string?

okay i have figured this much out,

Tsin(16.69) = m (v^2)/ r
T cos 16.69 -mg =0

i dont know how to solve for T though. i know it should be simple math, but i cant figure it out!

i have tried this

r(tsin 16.69) / v^2 = m
and Tcos16.69 / g = m

and then make them equal,

Tcos16.69 / g = r(Tsin16.69)/V^2

but now i am lost

2. Oct 18, 2007

### Staff: Mentor

What are the knowns and unknowns?

3. Oct 18, 2007

### cristo

Staff Emeritus
What values out of those you have written down do you know? At the moment you have two equations in four unknowns, so you will not be able to solve them!

4. Oct 18, 2007

### klm

oh sorry! i know that r=.3 and m =.2

but i just realized that if i know those, i can just plug them into the 2nd equation and find T...i think

5. Oct 18, 2007

### Staff: Mentor

What I would do is immediately combine these equations to eliminate T and solve for v. Then you can plug in that answer for T.

(If you write the second equation as T cos 16.69 = mg, it might be easier to see how to combine them.)

6. Oct 18, 2007

### klm

^ooh i understand what you are saying. thank you!