# Homework Help: Need Help please

1. Feb 5, 2009

### noaamari

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

A log is floating on swiftly moving water. A stone is dropped from rest from a 75-m high bridge and lands on the log as it passes under the bridge. If the log moves with a constant speed of 5.0 m/s, what is the horizontal distance between the log and the bridge when the stone is released?

2. Relevant equations

Not really sure how to start off the problem, would appreciate if anyone could help me on the problem.

3. The attempt at a solution I tried using the equation VF^2=Vi+2a(Xf-Xi)

2. Feb 5, 2009

### Hannisch

A good place to start is to find the time it takes for the stone to fall those 75m. How can you relate that time to the movement of the log?

3. Feb 5, 2009

### noaamari

Not really sur how to find the time when the only given information is that it is 75m high from the log. If I need to find the time I also need the velocity or acceleration. So how can I do that?

4. Feb 5, 2009

### LowlyPion

You know the height.

You know gravity.

x = 1/2*g*t2

5. Feb 5, 2009

### noaamari

Okay so i followed the equation and got apporoximately 3.9 secs then what equation can I use next to relate to horizontal distance?

6. Feb 5, 2009

### LowlyPion

How fast again was the log moving?