## 1.39 Help

$\lambda=\frac{h}{p}$

Ashley Davis 1I
Posts: 57
Joined: Fri Sep 29, 2017 7:04 am

### 1.39 Help

Could someone help me with 1.39? My units don't cancel out properly. I thought J = kg * m^2 * / s^2? But in my equation I have one kg on top, two meters, and only one second. This is what I entered:

wavelength = (6.626 x 10^-34 kg • m^2 • s^-2) / (0.15 kg)(41 m)

manasa933
Posts: 72
Joined: Fri Sep 29, 2017 7:04 am

### Re: 1.39 Help

Hey,

So first convert the mass into kgs and the mph to m/s so they're in SI units.

Then use De Broglie's equation:
L=h/p or L=h/mv
We know the mass and velocity.
h ---> Planck's constant

Janine Chan 2K
Posts: 71
Joined: Fri Sep 29, 2017 7:04 am

### Re: 1.39 Help

I think the only thing you're missing is that 41 should be in m * s^-1, not just meters.

Sheel Shah 1H
Posts: 33
Joined: Fri Sep 29, 2017 7:04 am

### Re: 1.39 Help

Are we expected to know the conversion from miles to kilometres? It's not on the equation and constant sheet either!

Elika Asis 3C
Posts: 19
Joined: Fri Sep 29, 2017 7:07 am

### Re: 1.39 Help

Sheel Shah 1H wrote:Are we expected to know the conversion from miles to kilometres? It's not on the equation and constant sheet either!

I don't think we are (I think, or at least hope, that on the midterm or on the final, conversion factors that are a little bit more out of the blue will be given) but it might be super helpful just to know a few conversion factors like that to help speed up the process :)

Navleen Bajwa 3A
Posts: 20
Joined: Fri Sep 29, 2017 7:06 am

### Re: 1.39 Help

First convert the mass into kilograms and the velocity into ms^-1. You placed the numbers correctly into the equation, but the only thing you are missing is the 41ms^-1.