# Homework Help: Find the De Broglie wavelength

1. Apr 23, 2007

### SamTsui86

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

Johnny Jumper's favorite trick is to step out of his high-rise window and fall 56.0 m into a pool. A news reporter takes a picture of 70.0 kg Johnny just before he makes a splash, using an exposure time of 7.00 ms. Find the following.

(a) Johnny's de Broglie wavelength at this moment

2. Relevant equations

wavelength = h / (mv) v = x/t

3. The attempt at a solution

so I know figured out v which is just 56 m / .007 s = 8000 m/s
I know m = 70 kg
I plug it in to the equation wavelength = (6.63e-34) / ((8000)(70)))

I got 1.18e-39 m. It saids I am wrong, plz help
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Apr 24, 2007

### mezarashi

I'm slightly confused by your first step in which you divide the 56 meter height of the building by the camera's shutter speed to come at 8 thousand meters per second.

If you are trying to calculate his speed at impact, this is not the right way to do it.

3. Apr 24, 2007

### chaoseverlasting

You can calculate his speed but using: $$v^2=2gs, (u^2=0$$ in this case). You can use $$\lambda=\frac{h}{\sqrt{2mT}}$$ where T is the kinetic energy of the man at that point.

The virtue of using $$v^2$$ for this equation is that you can use it directly to calculate the kinetic energy. I think thats it, though I dont know how the shutter speed plays in. The man is accelerating with 'g' at that point if it helps though.