Coin 2 is further away than coin 1.
I believe centrifugal acceleration is done by friction. So fs=us*m*g. Fc=mv^2/r.
Suppose coin 2 is at radius 2(r1), (r1) being the distance from center of coin 1.
angular velocity 1= r1(sqroot(us*g))
angular velocity 2=2r1(sqroot(us*g))
So, I conclude that coin 1 must be thrown off first. HOWEVER, the answer manual says it is coin 2, which is an obvious answer for me too. But, I can’t seem to be able to prove it.