The centripetal acceleration is given by
[tex]a_c = \frac{v^2}{r} [/tex]
where v is the tangential speed and r the radius of the circular orbit.
For the car in this problem, [tex]a_c = 15.625 m/s^2[/tex] and r=40 m, so we can re-arrange the previous equation to find the velocity of the car:
[tex]v= \sqrt{a_c r}= \sqrt{(15.625 m/s^2)(40 m)}=25 m/s [/tex]
