# kinematics question 3

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A stone is released from an elevator going up with an acceleration a and speed u. The acceleration and speed of the stone just after the release is
(A) a upward, zero (B) (g-a) upward, u (C) (g-a) downward, zero (D) g downward, u

+1 vote
by (9.9k points)

### Explanation:  As soon as the stone is released from the elevator the acceleration 'a' of the elevator has no effect on the stone, it is now only under the influence of the gravitational pull. So only acceleration due to gravity 'g' acts.

asked Jul 17, 2017 in Physics by (1.3k points) How the velocity is u???
by (64.9k points)
While the stone is still travelling on the elevator, there are two forces acting on it, the force from the elevator to the stone, as well as the weight due to gravity.
The moment the stone leaves the elevator, it becomes a free falling object. The elevator stops giving a force to the stone, and the only force remaining is its weight due to gravity.
From this you can see that as the only force is W = mg, the acceleration felt by the stone will be g.

While it is true it will be travelling upwards initially due to its momentum, its initial speed does not matter, as the only force that is acting on it would be force due to gravity, so its acceleration experienced will simply be g.