What are the unknowns in a simple pendulum problem and how can they be solved?

[SciencePF]

Homework Statement

A sphere of mass 0,5 kg bounces from 2 extreme positions like a pendulum. When it makes a 25º with vertical the sphere is 20 cm high from equilibrium position and the tension value is 5,5 N.

Find:

- Total acceleration
- Length of the wire
- velocity modulus in that position
- minimum value for the tension in the wire

Homework Equations

T-mgcos[tex]\theta[/tex]=mv2/r
-mgsin[tex]\theta[/tex]=ma

The Attempt at a Solution

5,5-0,5+10cos25=0,5v2/r
-0,5*10sin25=0,5at

in the previous expressions v2 is v square and at is tangential acceleration

I don't know how to find v or r (the length of the pendulum). Can you help? Thanks

 

[katchum]

I think you could introduce: mgh = 1/2mv^2 to find v.
And somehow you use 20cm to calculate h.

 

[SciencePF]

i think that your suggestion only gives v if the pendulum has started its motion from an angle that corresponds to h=20 cm.

 

[SciencePF]

Hello, friends!
A great help would be if someone can say that this problem has a solution!

 

[Shooting Star]

Drawing a diagram and dropping a perp on the vertical at the mean position from the bob when it's at 25 deg, r-20 = r*cos 25 gives you r, where r is the length of the pendulum. Now find v.

 

[SciencePF]

Thanks very much to all :)