1. Oct 8, 2013

JenL

1. The problem statement, all variables and given/known data
Jackie's team bats later in the day. When Jacki strikes the ball, she hits it badly and it travels straight up.

2. Relevant equations
Explain whether the forces are balanced or unbalanced at the highest point.

3. The attempt at a solution
I thought it was balanced as the ball will be stationary for a moment at the highest point but that was wrong...

2. Oct 8, 2013

PhanthomJay

It is momentarily stationary, yes, but what are the forces acting on it at that point? Is there a net force?
And oh, welcome to PF!

3. Oct 8, 2013

JenL

the question doesn't say if there is a net force but the force acting on the ball are gravity and the force from the bat

4. Oct 8, 2013

PhanthomJay

At the instant the ball leaves the bat, the bat is no longer in contact with the ball, so therefore it no longer exerts a force on the ball. So during the flight of the ball, what force (or forces) acts on it? In particular, identify the force(s) acting on the ball at the highest point. Is there an unbalanced net force acting on the ball at that point?

5. Oct 16, 2013

JenL

The question does not say if there is a net force or what forces are acting on the ball

6. Oct 16, 2013

haruspex

Quite so, since that is what you are expected to determine. When the ball is lying on the ground, what forces are acting on it? If a ball is falling through the air, what forces are acting on it? What equation do you know relating acceleration of a mass and the net force on it?

7. Oct 16, 2013

JenL

Fnet= ma, but I do not understand how this equation will relate to the problem because then the acceleration would be 0 at the highest point. So Fnet= 0 meaning forces acting on the ball are balanced and the answer said that the forces are unbalanced.

8. Oct 16, 2013

Khemical

Hey There JenL, I think that the acceleration would not be 0 because the gravitational field strength will make the ball accelerate at -10m/s^2 downwards

9. Oct 16, 2013

haruspex

The velocity is zero at the highest point, but not the acceleration.
You did not answer my question about the forces on a ball lying on the ground. Clearly that does not accelerate, so the forces are balanced in that case. What are they?

10. Oct 17, 2013

JenL

Thank you Khemical, that helped. Haruspex, The forces on a ball lying on the ground would be reaction and gravity which would be equal and so balanced. I think I understand the acceleration bit now and the question because wouldn't the acceleration be 10ms^-2 due to the force of gravity. So then Fnet would be unbalanced?

11. Oct 17, 2013

haruspex

Exactly.

12. Oct 18, 2013

Thank you :)