The force of friction is given in the scenario:
Force = 500 Newton
and the mass of the runner is 60 kg
To find the acceleration we need to use the relation between force, mass, and the acceleration of the object:

Where 'F' represents the force, 'm' represents the mass, and 'a' represents the acceleration.
Plugging the value of variables we get:

Solving for 'a' (acceleration) we get:
Newton/kilogram or meters/ second squared
So the acceleration of the runner is 8.33 meters/ second squared.