Page **1** of **1**

### SI Units

Posted: **Thu Oct 17, 2019 6:06 pm**

by **salvadorramos3k**

So since the wavelength in question 1B.23 is given in pm and we know that the constant for 1 amu is 1.67493x10^-27 kg, does that mean that before we do any calculations we have to convert them to meters and grams? Also, how would the cancellations of the units work for that? I know that velocity is m/s, but then there are J in the equation and I'm not seeing what is going to cancel them out. I know this is a lot, let me know if I have to clarify my question. Thank you so much! :)

### Re: SI Units

Posted: **Thu Oct 17, 2019 6:41 pm**

by **Sarah Zhari 1D**

If you are using the equation wavelength=h/p, you need to convert the wavelength to metres, but you do not have to convert the mass of the neutron to grams, and you have to leave this mass in kilograms because the units for momentum(p) is kgm/s

### Re: SI Units

Posted: **Sat Oct 19, 2019 1:34 pm**

by **Amanda Lin 2I**

The wavelength would need to be in meters, but the mass of the neutron can stay in kg because that is the SI unit for mass.

Also, 1 J = 1 kg*m^2*s^-2, so the units would cancel out leaving you with m/s for your final answer.

### Re: SI Units

Posted: **Sat Oct 19, 2019 1:54 pm**

by **Robert Tran 1B**

Since 1 J = 1 kg*m^2/s^2, this will allow the kg and m to cancel out. Thus, you should convert the pm to m, but you can leave the kg alone so that it cancels out. Just make sure that your units always cancel out to determine whether you need to convert them or not.

### Re: SI Units

Posted: **Sat Oct 19, 2019 1:55 pm**

by **Robert Tran 1B**

Since 1 J = 1 kg*m^2/s^2, this will allow the kg and m to cancel out. Thus, you should convert the pm to m, but you can leave the kg alone so that it cancels out. Just make sure that your units always cancel out to determine whether you need to convert them or not.