Is the acceleration of a projectile equal to zero when it reaches the top of its trajectory? If not, why not?

Question

Is the acceleration of a projectile equal to zero when it reaches the top of its trajectory? If not, why not?

Answer 1

A projectile is subject to a constant acceleration due to Earth's gravity.  The velocity of the projectile is what reaches zero at the top of the trajectory.

Answer 2

If it is going straight up the answer is yes, it will stop and then fall back.

However, if it is going straight up it will decelerate to the point where it starts to fall and will then increase in acceleration by the pull of gravity.

Answer 3

The acceleration of a projectile is always equal to the acceleration of gravity. It is a constant number and will not change. It WILL NEVER be equal to zero. What changes is the velocity of the projectile.

As it goes up, it is going against gravity it is slowing down. As it reaches the top of its trajectory, its velocity will be zero and at this point, it will start to come down.

Coming down, gravity pulls the projectile hence its speed increases as it is coming down.

Answer 4

because it is in earths gravitational field. So it is subject to an acceleration of g at all times.

If a heavy thing like a car was rolling backward and your job was to make it go forwards you would push on the back of it with a force F. It would keep rolling backwards but would eventually slow down and stop before it started rolling forwards. You were pushing with a force F the whole time. Since F=ma the acceleration was constant the whole time. The fact the the car was stopped at some point, equivalent to the projectile at the top of its trajectory, doesnt change the fact that is was being pushed the whole time. If you made a graph of its velocity you would see that it was positive then it crossed zero and became negative. Since acceleration is the derivative of velocity the fact that it crossed zero doesnt matter as long as its slope was finite there is finite acceleration.