Answer
Please see the work below.
Work Step by Step
We know that the centripetal acceleration is given as
$a=\mu g$
We plug in the known values to obtain:
$a=(0.71)(9.8)=6.958\frac{m}{s^2}$
The initial speed is given as
$v_i^2=v_f^2+2ad$
We plug in the known values to obtain:
$v_i^2=(\frac{25}{3.6})^2+2(6.958)(47)=701$
$v_i=26.5\frac{m}{s}$
