# Physics HW- Falling Bodies

1. Nov 6, 2013

### Medgirl314

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

A diver steps off a platform 30m above the water. With what speed does he hit the water?

2. Relevant equations
v=intial v+at

3. The attempt at a solution

I reached an answer of 2.47 seconds, but I can't see how I got there anymore! Is this answer correct?

Thank you very much!

2. Nov 6, 2013

### tiny-tim

Hi Medgirl314!

You need to learn the standard constant acceleration equations.

In this case, you know vi and a and s, and you want vf

so the equation to use is … ?

3. Nov 6, 2013

### Medgirl314

I think I used several equations, but they faded a bit. Blasted erasable pens. Since it's a fairly new concept, my physics teacher doesn't want me to have them memorized yet. I think I used y=y0+v0+1/2 at^2 and t^2=2y/a .

The answer seems plausible. Did I get it right?

Thanks again, and thanks for the link!

4. Nov 6, 2013

### tiny-tim

(try using the X2 and X2 buttons just

Hi Medgirl314!

(try using the X2 and X2 buttons just above the Reply box )
rubbish!

there's only 3 basic equations, memorise them and everything will be much simpler!
you mean y=y0+v0t + 1/2 at2

(and the second one is just another version of the first one, with zero constants)

on this forum, you need to show your calculations, not just the answer

5. Nov 6, 2013

### Medgirl314

Oh! I'm sorry! My answer was actually 24.2 m/s. I gave you a different part that I used to find that answer. I think I used t=√2y/a, and got t=√2.3 m/9.8 m/s^2, giving a time of 2.47 seconds. Then I used v=vo+at , plugging in my numbers to get v=0+9.8 m/s^2(2.42 s), and then got my answer of v=24.2 m/s. Is this better? Thank you!

6. Nov 6, 2013

### tiny-tim

HI Medgirl314!

(never use . for multiplication … use x or * or brackets )
yes, that's correct (you meant 30 not 3)

but quicker would have been to use vf2 = vi2 + 2as

7. Nov 6, 2013

### Medgirl314

Thank you! I must have used a dot for multiplication on my paper and didn't notice that it was 30, not 3.0!