Correct Answer - Option 3 : 82 mm

__Concept:__

The mean radius of friction face assuming the uniform pressure condition is given by:

\({R_m} =\frac{2}{3}\left( {\frac{{r_o^3\; - \;r_i^3}}{{r_o^2\; - \;r_i^2}}} \right)\)

Where r_{o} & r_{i} are the external and internal radii of the clutch.

__Calculation:__

__Given:__

r_{o} = 100 mm, r_{i} = 60 mm.

\({R_m} =\frac{2}{3}\left( {\frac{{r_o^3\; - \;r_i^3}}{{r_o^2\; - \;r_i^2}}} \right)\)

\({R_m} =\frac{2}{3}\left( {\frac{{100^3\; - \;60^3}}{{100^2\; - \;60^2}}} \right) = 81.67\; mm\) ≈ 82 mm

**∴ The mean radius of the friction face assuming the uniform pressure condition is 82 mm.**