A cylindrical cell is given an initial speed of v₀ at the bottom of a smooth ramp that makes an angle of 20° with the horizontal. The cell rolls up 1.3 m without slipping before stopping briefly and rolling down. The roughness of the ramp is increased, and the cell is given the same initial speed of v₀ at the bottom of the ramp. The cell rolls up without slipping a distance of 1.1 m. Calculate the coefficient of rolling friction of the rough ramp.