Physics question?

Question

A ball is thrown straight up. what will be the instantanious velocity at the top of it's path? What is the acceleration at it's preak? Why are your answers diffrent?
I DONT GET IT! I THOUGHT THEY WERE THE SAME!

notice i said "Why are your answers diffrent?" No one has answered that part yet

Answer 1

At the top of it's path, the ball pauses before starting back down... at that instant, it is not moving and the velocity is zero.

The acceleration acting on the ball is g (earth gravity) and that is always present. It first slows the ball to a stop and then speeds the fall back to the ground.

Imagine someone running away from you and you start pulling them backward with a rope around their waist. If you pull hard enough continuously, they will slow to a stop, then start moving backward toward you. You were pulling the entire time and reversed their motion. And notice that you were always pulling in the same direction, like gravity pulls toward the ground.

Aloha

Answer 2

At the top of it's path, the instantaneous velocity is zero. The definition of instantaneous velocity is dx/dt where dx is the displacement in a time dt that tends to zero. Since during that split second at the top, dx=0 (ie, it is stationary) the velocity is also zero.

Another definition of acceleration is that it is the force acting per unit mass of a body. When a ball is thrown into the air, the only force acting on it is gravity. Here we are neglecting other forces exerted by the fluid around it, ie the air. Also assuming that the ball is not thrown very high, this force of gravity remains constant throughout it's flight. Since the mass is also invariant, the acceleration is also constant, irrespective of whether the ball is travelling up or down. The value of this accleration is generally 9.81 m/s², although it varies with height and location.

Answer 3

I gave that a lot of thought a long time ago. I came to the conclusion that the ball instantaneously reverses direction at the top, that it does not dwell at the top for any duration of time. It is the same as a pendulum in a clock which measures time. Time is delineated only by the motion of the pendulum. It never really comes to a stop; it is going one direction or the other. The acceleration is constant, but the direction reverses at the top. So, the motion never stops.

Edit: it does not stop for a "split second." There is no way you could measure that "split second," because time is measured by motion. Think about it. The "top" is just another point along the trajectory. It does not dwell for any length of time at any point along the trajectory.

Edit: whoever gave my answer the thumbs down simply does not like an objective description of reality. So, go with your fantasy or whatever.

But Mathew KE: there is no such thing as a point of time. Time is always an interval between two points. There can be no delta t at the top of the trajectory, because delta is the difference between two points.

Answer 4

At the top, of course, its 0. (it stops, since its going up and then at some point starts going down). This much I suspect you already knew. Now as for acceleration not being zero at the top.. think about it like this.. if it *were* 0 at the top, the ball would be feeling no tug by gravity to return to the ground and would simply remain there (indeed, if there were no gravitational acceleration at all, it would go up indefinitely). Think about the fact that the ball is slowing down as it approaches the top of its trajectory. Slowing down represents an acceleration towards the earth, but since the ball's still got some speed, its gonna take a few seconds before we see the ball slow down to a stop, then begin going downward.

Answer 5

The instantaneous velocity at the very top is 0 m/s or ft/s because the ball changes direction at the very top of the path, that is where it stops for a moment. The acceleration is the same throughout the whole path including the peak. It's 9.8 m/s/s or 32ft/s/s -- the force of gravity or acceleration of gravity.

Answer 6

Well the velocity at the very top goes to zero, because as soon as you throw the ball up it starts slowing down. At the very top it stops commpleatly then it starts speeding back down to the floor. The acceration goes from -9.8 because when you throw it up its decreasin in speed negitivewise and then it turns +9.8 right after the top because now its speeding up.

Answer 7

the acceleration at it's peak will be 0. this is because the ball will have to stop in mid air for a split second before dropping which means that there is no acceleration just before it changes direction.

Answer 8

For the split second that it hovers there, the acceleration is -9.8m/s...exactly the opposite of the acceleration due to gravity, allowing it to hover.

The velocity is 0, because for that split second, it is not travelling in any direction at any speed, it is frozen there.

Answer 9

velocity at peak: 0 m/s(b/c its not going up or down)
acceleration: -9.81 m/s^2 b/c thats the acceleration of an object due to gravity.

Answer 10

top of it's path: 0 -> the ball stalls.
the acc depends on your force when throwing it. That applies when throwing it upwards, when throwing it down (into a hole) the gravitational acc changes every second and reaches 0 in the middle of the Earth ;)