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### Question from module

Posted: **Sat Oct 12, 2019 11:02 pm**

by **Isabel Day 1D**

If a problem gives me only the velocity of the ejected electron and the work function for the metal, how do I find the kinetic energy? I can't figure out how to do it without needing the mass of the electron or the frequency of the incoming photon.

This is the problem:

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1.

It asks for the kinetic energy of the ejected electron.

### Re: Question from module

Posted: **Sat Oct 12, 2019 11:35 pm**

by **Timmy Nguyen Dis 1I**

You could just use the mass of the electron, since it's going to be one of those numbers that are given on exams.

### Re: Question from module

Posted: **Sun Oct 13, 2019 9:45 am**

by **Maya Gollamudi 1G**

The kinetic energy of an electron is its mass x velocity. You can use the mass of an electron to find the KE, which is 9.11 x 10^-31 kg (the mass of an electron will be given to us on tests).

### Re: Question from module

Posted: **Sun Oct 13, 2019 2:58 pm**

by **Ashley R 1A**

You're going to use the equation E = 1/2 m v^2. In this case, E stands for the kinetic energy of an electron. The mass of an electron will always be constant at 9.109x10^-31 kg, it's on the formula sheet that we're given on tests.

### Re: Question from module

Posted: **Sun Oct 13, 2019 7:50 pm**

by **quresh3E**

I worked backwards and solved for the wavelength then inputted it into the E=H*C/v equation. Why is this wrong?

### Re: Question from module

Posted: **Sun Oct 13, 2019 11:23 pm**

by **Ian Morris 3C**

Timmy Nguyen Dis 3F wrote:You could just use the mass of the electron, since it's going to be one of those numbers that are given on exams.

Is the mass of an electron on the reference sheet?