Suppose that you toss a rock upward so that it rises and then falls back to the earth. if the acceleration due to gravity is 9.8 m/sec2,
what is the rock’s acceleration at the instant that it reaches the top of its trajectory (where its velocity is momentarily zero)?
assume that air resistance is negligible.

a)the acceleration of the rock is zero.
b)the rock has an upward acceleration of 19.6 m/s2.
c)the rock has a downward acceleration of 19.6 m/s2.
d)the rock has a downward acceleration of 9.8 m/s2.
e)the rock has an upward acceleration of 9.8 m/s2.