We present V -band CCD photometry of 65 RR Lyr variables from the globular cluster M5 .
We have estimated the basic physical parameters for 16 RRc stars and 26 RRab stars using a Fourier decomposition of the light curves of the variables .
The mean values of mass , luminosity , effective temperature and relative helium abundance for the RRc stars are measured to be { \cal M } = 0.54 ~ { } { \cal M } _ { \odot } , \log ( L / L _ { \odot } ) = 1.69 , T _ { eff } = 7353 K and Y = 0.28 , respectively .
For the RRab variables the derived mean values of absolute magnitude , metallicity and effective temperature are : M _ { V } = 0.81 , { [ Fe / H ] } = -1.23 and T _ { eff } = 6465 K. We find that the V amplitude of an RRab star for a given period is a function of metal abundance rather than Oosterhoff type .

We find significant problems with the calibration of both the zero point and the scale of the luminosities measured with the Fourier technique .
The apparent distance modulus derived from RRc stars is equal to 14.47 \pm 0.11 and it is in good agreement with recent determinations .
On the other hand distance modulus obtained from the sample of RRab stars ( calibrated by the Baade-Wesselink observations of field RR Lyr variables ) is significantly smaller and equal to 14.27 \pm 0.04