# Stumped on long problem

1. Oct 16, 2008

### a2k22

1. The problem statement, all variables and given/known data

I need someone to walk me through this problem. I know its a bit lengthy, but my teacher hasn't explained how to do this, and I'm completely stumped.

A ball of mass 0.6 kg, initially at rest, is
kicked directly toward a fence from a point
20 m away, as shown below.
The velocity of the ball as it leaves the
kicker’s foot is 18 m/s at angle of 62 ◦ above
the horizontal. The top of the fence is 9 m
high. The kicker’s foot is in contact with the
ball for 0.06 s. The ball hits nothing while in
flight and air resistance is negligible.
The acceleration due to gravity is 9.8 m/s2.

Determine the time it takes for the ball to
reach the plane of the fence. Answer in units
of s.

Hint: Consider the diameter of the ball to be
negligible.
How far above the top of fence will the ball
pass? Answer in units of m.

What is the vertical component of the velocity
when the ball reaches the plane of the fence?

2. Relevant equations

No clue...

3. The attempt at a solution

My teacher just randomly decided to give us this, even though we haven't learned it. And I'm not exaggerating, and therefore I'm completely lost.

2. Oct 16, 2008

### Aftermarth

haha poor you with this teacher :(

to reach the plane of the fence you need to find the time (in seconds) to travel the necessary horizontal distance

3. Oct 16, 2008

### a2k22

Can I just get an answer please? I have no idea how to do this. I would really like to go to bed. I'll try and figure out the problem tomorrow. I know you are trying to help me, and I appreciate it. It's just been a very tiring day, and I have to get up early tomorrow again.

Thank you.

4. Oct 16, 2008

### LowlyPion

OK. You can do it anyway.

What are the x,y components of velocity. (Hint: 62 degrees)

Knowing the y velocity what is the equation for y position as a function of time?
Likewise for x.

With the x,y functions of position as a function of time you can figure out the rest.

Need formulas?
https://www.physicsforums.com/showpost.php?p=905663&postcount=2

5. Oct 16, 2008

### LowlyPion

No.

You can do it if you put in the effort. People will help if you get stuck.

Sorry but forum rules are no effort = no answers.

6. Oct 16, 2008

### a2k22

err...2.37 seconds until the ball reaches the fence? correct?

7. Oct 16, 2008

### Aftermarth

sounds good to me

8. Oct 16, 2008

### a2k22

What about the rest? I'm really confused on the magnitude part.

9. Oct 16, 2008

### Aftermarth

ill get back to you asap
for now i need to go to my Dynamics class

good luck
if u need sleep go get it.. u will think better when you are rested :)

10. Oct 16, 2008

### a2k22

It's due tomorrow, 6 AM, its an online hw.

11. Oct 16, 2008

### a2k22

And I missed a question:
Determine the magnitude of the average
net force exerted on the ball during the kick.