If an object is dropped how can its velocity be zero but acceleration be 9.81?Watch this thread
also how would you work this out from a velocity time graph of a falling object?
The acceleration is due to gravity which is a constant force acting on the object - even when it is stationary. i.e. acceleration = force / mass and since the force acting and the mass of the object are both constant, acceleration must also remain constant. the gravitational force is held in check by the equal and opposite reaction of the restraint holding the object stationary.
If the object is in motion (say thrown vertically), the gravitational force will cause deceleration and at some point the object will reverse direction and accelerate towards the ground. NB at the apex of travel, the object must at pass through a point of zero velocity.
From a velocity / time graph, zero velocity is indicated by no gradient. i.e. the graph is a flat line or at a point of inflection where the gradient is zero.