Question

1.What is the acceleration of a projectile when instantaneous vertical velocity is zero at the top of its trajectory?

Answer 1

The acceleration is always -g, in the downward direction if distance is measured positive upwards.

Answer 2

it depends... when you talk about acceleration of object going downward, its -g... when acceleration going up, example an object is thrown, i think its 0.

ax=o; ay= -g