Physics question!!! please help!?

Question

A rock is thrown at some angle above the horizontal with a certain velocity. It reaches its highest point and starts falling down. What is the magnitude of the acceleration of the rock at the highest point of its trajectory?

Answer 1

Assuming you are on Earth (and no mini-rockets are attached to the rock), the magnitude of the acceleration of the rock at its highest point will be approximately 9.8 m/(s^2).

Note: She asked for _magnitude_, so no minus (-) sign is necessary.

Answer 2

the answer is 9.8 m/s^2.  

In order to make anything move from rest you must apply a force to it another way to say that is that you must give the object some kind of acceleration.  

When the rock is at its highest point that means that the velocity of the rock moving upward is zero (Note: I said velocity is zero not acceleration).  In order to get the rock moving again there must be a force acting on the rock.   Are there any force action on the rock?  Think for a sec......The only force action on the rock is due to gravity.  Think about that, no matter where you put the rock gravity will be the only for acting on it.   Put it in your pocket, throw it in the sky, put it in a box, drop it off a cliff.  The point is that the acceleration of the rock near the surface of the earth will always be 9.8 m/s^2 unless another force acts on it.   (Note: once the rock leaves your hand you are no longer applying a force to it. The rock will have all its energy already from what you gave it.  At that point the only force to act on it is gravity)

Answer 3

zero

Answer 4

At any point along the trajectory, the acceleration is a constant (g), due to the downward pull of gravity.  So the acceleration is -32 ft/sec/sec.