Energy in kj or j when solving a problem?

Moderators: Chem_Mod, Chem_Admin

Jennifer1E
Posts: 25
Joined: Fri Jun 23, 2017 11:39 am

Energy in kj or j when solving a problem?

Postby Jennifer1E » Sun Jul 09, 2017 3:58 pm

Just for clarification. When solving a photoelectric effect problem, if the threshold energy is given in kj should it be converted to j when finding the kinetic energy?

Davalanya 1F
Posts: 23
Joined: Fri Jun 23, 2017 11:39 am
Been upvoted: 1 time

Re: Energy in kj or j when solving a problem?

Postby Davalanya 1F » Sun Jul 09, 2017 5:42 pm

I think it has to be changed to Joules always because when we cancel units for energy we are left with J, and if we leave it in kj we have to change the rest of the other units to get the kj in the final answer.

JD Malana
Posts: 21
Joined: Wed Nov 16, 2016 3:02 am

Re: Energy in kj or j when solving a problem?

Postby JD Malana » Sun Jul 09, 2017 7:09 pm

I agree. Also, I would just set up the problem in the standard units of measurement (J for energy, nm for wavelength, etc.) to avoid multiple conversions down the road.

Sohini Halder 1G
Posts: 58
Joined: Thu Jul 13, 2017 3:00 am
Been upvoted: 1 time

Re: Energy in kj or j when solving a problem?

Postby Sohini Halder 1G » Wed Oct 11, 2017 4:03 pm

Set up the problem using J because that is the standard unit for energy, but you can either leave your answer in J or convert to kJ if youu want.

Jessica Jones 2B
Posts: 80
Joined: Fri Sep 29, 2017 7:04 am

Re: Energy in kj or j when solving a problem?

Postby Jessica Jones 2B » Wed Oct 11, 2017 6:10 pm

I have a question regarding units. How do kg cancel out when divided by J?

Curtis Tam 1J
Posts: 105
Joined: Thu Jul 13, 2017 3:00 am

Re: Energy in kj or j when solving a problem?

Postby Curtis Tam 1J » Wed Oct 11, 2017 10:21 pm

504909047 wrote:I have a question regarding units. How do kg cancel out when divided by J?


J=kg*m^2*s^-2

So if, for example, you get a value joules divided by kg, then that would leave you with m^2*s^-2. Hope that helps!

Sophia Kim 1C
Posts: 51
Joined: Fri Sep 29, 2017 7:04 am
Been upvoted: 1 time

Re: Energy in kj or j when solving a problem?

Postby Sophia Kim 1C » Thu Oct 12, 2017 11:49 am

I would use J since it makes the calculations simpler (since if you used kj you would need to change all of the j to kj so that all the units remain uniform) and if the answer asks for kj you can convert it as the last step of the problem.

Josh Moy 1H
Posts: 58
Joined: Thu Jul 13, 2017 3:00 am

Re: Energy in kj or j when solving a problem?

Postby Josh Moy 1H » Thu Oct 12, 2017 4:02 pm

If we have kg or km should we convert to g and m?

Daniel Rivas 3L
Posts: 32
Joined: Fri Sep 29, 2017 7:07 am

Re: Energy in kj or j when solving a problem?

Postby Daniel Rivas 3L » Thu Oct 12, 2017 5:02 pm

Josh Moy 1I wrote:If we have kg or km should we convert to g and m?

I think it depends on the problem. Sometimes it asks you for specific units to end up with. In that case, you should leave it in the desired units the question asks for. However if the question doesn't ask, then I think you can leave it in whatever units you choose. I tend to leave it in the units the question gives to me. For example if the question gives me 15 km and wants a distance answer, I will probably leave the answer in km.

204918982
Posts: 50
Joined: Fri Sep 29, 2017 7:04 am

Re: Energy in kj or j when solving a problem?

Postby 204918982 » Thu Oct 12, 2017 5:47 pm

Josh Moy 1I wrote:If we have kg or km should we convert to g and m?


If the problem specifically asks you to convert to g or m then you should, but if it doesn't ask you to then I would suggest just keeping the units that you are given in the problem.

kaitlindaugherty3L
Posts: 21
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

Re: Energy in kj or j when solving a problem?

Postby kaitlindaugherty3L » Thu Oct 12, 2017 8:50 pm

So should we put the answer in Joules even if the problem gives us the units in Kilojoules?


Return to “Photoelectric Effect”

Who is online

Users browsing this forum: No registered users and 0 guests