Answer
Nature of the surfaces.
Explanation
Friction is the the force that opposes motion between two surfaces that are in relative motion. If two objects are in contact, one of it or both must be in motion for friction to exist.
Friction is affected by a number of factors.
One is the weight of the object. The more the weight of the object the higher the friction between it and the surface.
The other factor is the nature of the surfaces. Rough surfaces contribute to high friction while smooth surfaces reduces the friction between surfaces.
Explanation:
(1) Every object moves in a straight line unless acted upon by a force. (2) The acceleration of an object is directly proportional to the net force exerted and inversely proportional to the object's mass. (3) For every action, there is an equal and opposite reaction.
Answer:
24.07415 rpm
Explanation:
= Coefficient of friction = 0.63
v = Velocity
d = Diameter = 4.9 m
r = Radius = 
m = Mass
g = Acceleration due to gravity = 9.81 m/s²
Here the frictional force balances the rider's weight

The centripetal force balances the weight of the person

Velocity is given by

Converting to rpm

The minimum angular speed for which the ride is safe is 24.07415 rpm