Units Cancelling Out

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

Units Cancelling Out

Postby Ashley Davis 1I » Wed Oct 11, 2017 6:55 pm

Could someone explain to me how units cancel out in equations like E = hv and E = 1/2mv^2? Do I even need to worry about it?

Julie Steklof 1A
Posts: 50
Joined: Thu Jul 13, 2017 3:00 am

Re: Units Cancelling Out

Postby Julie Steklof 1A » Wed Oct 11, 2017 8:07 pm

In E=hv, the units for h are Joules*seconds and units of v are seconds^-1. Multiplying these gives you Joules which is an appropriate unit for energy. In E=1/2mv^2, mass is measured in kilograms and velocity in meters per second. Joules is technically "short" for units of kg*m^2/s^2 which is what is given in this equation. Though you probably don't need to memorize this, it's useful to be able to check your work and make sure you used the correct given quantities.

soniatripathy
Posts: 50
Joined: Thu Jul 13, 2017 3:00 am

Re: Units Cancelling Out

Postby soniatripathy » Wed Oct 11, 2017 8:24 pm

For E=hv the units for h are (J*s) and the units for v are s^-1. When you multiply (J*s)x(s^-1) the seconds cancel out and you hare left with J, which is the unit used to measure energy.

Alexandria Weinberger
Posts: 51
Joined: Fri Sep 29, 2017 7:03 am

Re: Units Cancelling Out

Postby Alexandria Weinberger » Wed Oct 11, 2017 8:30 pm

The units in E=hv will cancel out because the units for Planck's constant is Joules*seconds and frequency is s^-1. Therefore you will be left with Joules, which is a unit for energy.


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