The maximum distance the man can climb without slipping is 6.4 m. This is calculated using the equation:
Friction force = μ × Normal force
Where μ is the coefficient of friction and Normal force is the weight of the man (500 N).
Friction force = 0.25 × 500 N = 125 N
Since the friction force must be equal to or greater than the man's weight, he can climb up to a distance of 6.4 m (125 N/500 N x 8 m).