# Homework Help: Problem help please

1. Oct 16, 2008

### a2k22

A man can throw a ball a maximum horizontal
distance of 138 m.
The acceleration of gravity is 9.8 m/s2 .
How far can he throw the same ball vertically upward with the same initial speed?

I figured out the initial speed to be about 280 m/s. Am I right? How can I finish the problem?

2. Oct 16, 2008

### Stovebolt

What steps did you take to determine the initial speed? I ran through the problem and got a much different answer.

3. Oct 16, 2008

### a2k22

I used the equation range equals (initial velocity squared * sin of 2 theta) divided by gravity.
range equals 180
theta equals 45 (this is the angle that will achieve the farthest range)
and gravity equals 9.8 (the negative sign is not needed)

And I did the problem again, and I got about 1352

4. Oct 16, 2008

### nasu

A good idea would be to show your solution.

5. Oct 16, 2008

### nasu

You forgot to take the square root this time.
Is the distance 138 or 180?

6. Oct 16, 2008

### a2k22

range is equal to 180, and yes, thank you. I always forget to square root. So it's about 36.77 m/s. Now how should I proceed?

7. Oct 16, 2008

### Stovebolt

Check the math on that one. It looks like you used 138 m for the range.

8. Oct 16, 2008

### a2k22

I got 42 m/s. What now?

Last edited: Oct 16, 2008
9. Oct 16, 2008

### Stovebolt

Given the initial speed and the final speed (at max height, v = 0), use the formula