Physics problem: how to do, thanks .?

(a) set max friction force = max centripetal force
10000 N = m(Vmax)²/r = 1500kg * (Vmax)² / 50m
Vmax = 18 m/s

(b) (i) decreasing radius leads to decreasing Vmax.
(ii) patches of oil would reduce the limiting friction, and that would lead to decreasing Vmax.

Hope this helps!