# Help with a new problem

1. Sep 23, 2006

### Alanf718

Ok Iam having problems again with yet something else.

The problem states that

A physics student with too much free time drops a water melon from the roof of a building. He hears the sound of the watermelon going splat 2.50s later. How high is the building? The speed of sound is 340m/s. You may Ignore air restiance.

Well I tried solving this by replacing t by

t= 2.5 - (deltaY/340);

but the book tells me a completely different answer. Can anyone show me how to do this one?

2. Sep 24, 2006

### Galileo

The time it takes until you hear the sound from the moment it is dropped is the times it takes the melon to fall to the ground plus the time it takes for sound to go from the ground to the top of the building.
Write down the equation for this and solve for the height.

3. Sep 24, 2006

### Alanf718

thats what i did with
t= 2.5 - (deltaY/340);

but I dont get the right answer

4. Sep 25, 2006

### Galileo

Why don't you elaborate on what you've done?
What method did you use exactly. You replaced t by 2.5 - (deltaY/340) in what equation? What answer did you get?

Try giving an expression for the amount of time it takes for the melon to drop to the ground. Then for the amount of time it takes for sound to travel up the lenght of the building.