Net force on ball from ground to top

[mocking]

Homework Statement

A ball is tossed up into the air. It reaches maximum height and comes back down.

What is the net force on the ball at the following situations:

a. The ball is moving upward as it is released.

b. The ball is at it's highest point. (when it comes to a stop i suppose)

c. The ball is moving downward.

Homework Equations

F = ma ?

The Attempt at a Solution

a. Force is up and decreasing.

b. Force is 0

c. Force is down and increasing.


Please let me know what you guys think. I have other problems also.

 

[Mentz114]

Welcome to the Forum.a is correct before release. b is wrong. Think again.
What is making the ball slow down and then come back down ?

C is formally correct but in practical terms, not so.

 

[Vijay Bhatnagar]

At all points the net force on the ball is the force of gravity i.e. its weight acting downwards (ignoring air friction). Because of this force only, the ball first decelerates coming to rest at the top most point and then accelerates downwards.

 

[drpizza]

Vijay just gave you the answer, so I'll see if I can help you understand it:

Let's suppose that at the very peak of it's flight, the force was equal to zero, as you initially thought. You also said the relevant equation is F=ma. Well, if F is zero, then the acceleration would also be zero. We already know that the velocity at that peak is zero. If the acceleration was also zero, then it'd just sort of stay there.

 

[mocking]

thank you for all your help! Mentz was wrong @ first but thank you for clearing up the rest.