Freefall Question?

Question

I got this question wrong on my test but I don't understand why.
-----An object is thrown up in the air, it reaches its max altitude. What is its acceleration at max altitude?

I put 0, the correct answer is -9.81. What I don't understand is how an object that is not moving can have an acceleration. The object is at rest, therefore I don't understand how it can feel the effects of gravity at the highest altitude. Now if the object fell for even .000000000000000001 seconds I could see how gravity would cause it to freefall. But I don't see how acceleration can pertain to an object that has no velocity.

Answer 1

The velocity is 0 at max h, but Gravity is ALWAYS acting on an object...thus the object was moving and gravity was acting down upon it, hence -9.81m/s^2

Gravity = Acceleration in respect to free fall motion

Answer 2

Please understand their relationship is quite the same as velocity to distance for accelaration to velocity: velocity is the change of distance w.r.t. time, and accelaration is the change of velocity w.r.t. time. At a start point, say, of a distance jumping, distance is zero, but velocity is NOT necessary to be zero. Now at the highest point, velocity is zero, but gravity never get turned off.