If I remember correctly, the correct answer is either:
A. Electrostatic
or
B. Gravitational
Using the second Law of Newton, F = m * a, you know that acceleration is maximum when the force is maximum.
Using Hooke's Law, F = K Δx, you know that the force is maximum when the displacement from the equilibrium (Δx) is maximum.
So the answer is that the acceleration is maximum at the maximum amplitude x = a.
B. The number of coils of wire around the core
P=IV
V=IR
P=I(IR)
P=I²R
375=5²R
R=375/25
R=15
