# Homework Help: Forces acting on two objects

1. Oct 12, 2005

### watarn

Hi, can anyone give me some help on the following question:

A basketball player is getting ready to jump, what are the forces acting on both the basketball player and the ground as he is jumping but before his feet leaves the ground.

I was also required to draw 2 free body diagrams...

thanks

-edit

well, actually i know that on the player, theres the force of gravity pointing down, and another applied force with a greater magnitude pointing upwards, im not sure whether's still a normal force.

and on the ground, there's an applied forced by the player acting downwards, is that all?

Last edited: Oct 12, 2005
2. Oct 12, 2005

### Tom Mattson

Staff Emeritus
We'll help, but only after you show how you attempted the problem. That is stated in those guidelines that you agreed to, but evidently did not read.

3. Oct 12, 2005

### ranger

You didnt even try. http://www.glenbrook.k12.il.us/gbssci/phys/Class/newtlaws/u2l2c.html [Broken] is some help with free body diagram.

Last edited by a moderator: May 2, 2017
4. Oct 12, 2005

### watarn

sorry, i wasnt sure about the rules... i've edited my post already
and i just want to make sure whether i got all the forces right before i draw my fbd, thanks

Last edited by a moderator: May 2, 2017
5. Oct 12, 2005

### ranger

Well if he is still on the ground, then there is normal force.

Normal Force:perpendicular force that a surface exerts on an object with which it is in contact. For example, if I ress a book in a flat surface, there is Normal force.

6. Oct 12, 2005

### Tom Mattson

Staff Emeritus
That applied force with the greater magnitude is the normal force. That's what pushes him off the ground.

Think about it: What does Newton's third law say? It says that for every action there is an equal and opposite reaction. You've got a system that includes only the man and the Earth. You've got two forces acting on the man, and only one on the Earth. That can't be all. You're missing one force acting on the Earth.

7. Oct 12, 2005

### watarn

so on earth, its the normal force exerted by the player or should i still call it the applied force?
is the force of gravity the one that i missed on the ground?

and one more thing, for the player, i can express it as a particle or a block on the fbd, how should i represent the earth though?

8. Oct 12, 2005

### ranger

Normal force is not exerted on the surface by an object, it is exerted on the object by the surface.

When you make that free body diagram, just represent the baseball player as a block and the ground as a horizontal line. Refer to that link that I gave you earlier.

9. Oct 12, 2005

### Tom Mattson

Staff Emeritus
Yes. The man attracts the Earth with a force that is equal to and opposite of the force with which the Earth attracts the man.

Other than that: Do what ranger said.