(20 10? As shown in the figure, an object falls from A and then compresses the spring to the lowest point. The maximum acceleration in the process is a 1, and the kinetic energy is the largest.

(1) When an object falls from A, the spring is compressed until the elastic force equals gravity:

The downward speed reaches the maximum, and then the object still moves downward due to inertia.

And continue to compress the spring kx > mg at this time.

Suppose that the kinetic energy of an object at the moment when it just touches the spring is E', obviously E' > 0.

Then when the object contacts the spring and the speed becomes zero, the maximum acceleration at this time is a 1.

The deformation of the spring is x.

Obviously, in this process, gravity does act on mgx.

The elasticity of the spring does negative work w,

According to the kinetic energy theorem, we can get e ′+mgx = w.

(2) When an object falls from B:

Let the instantaneous kinetic energy of the object contacting the spring be e ",because the release height HA < HB,

Obviously, e "> E "

Let e "= e'+△ e.

When the object falling from B reaches X,

E'+mgx=W is satisfied, and the object still has some kinetic energy △E,

So the object will continue to move down,

Continue to compress the spring, and the elasticity of the spring will increase.

So the acceleration a2 > a 1 at this time.

(3) When the kinetic energy is maximum, the elastic force of the spring is equal to the gravity of the object, and the resultant force acting on the object is zero.

In both cases, the length of spring compression is equal, so what is the elastic potential energy when the kinetic energy is maximum in both cases? E 1=E2

So choose: C.