# Two Strings and Two Boxes

There are two boxes of weights 1.0 kg and 2.0 kg. There is a string called string2 connecting the two boxes. There is another string called string1 connected only to the 2.0 kg box. I am not sure if the tension acting on the 2.0 kg box from string1 is greater than, less than, or equal to the tension acting on the 2.0 kg box from string2. Can this even be determined from the given information? I initially thought that they were equal to, but I was told that I was incorrect by a friend that knew the answer (but didn't care to explain, and didn't tell me the correct answer--that wasn't very nice of him).

I am almost 100% sure that Newton's 3rd law applies to this, but I am not sure how to apply it.

Thanks very much for any responses, and please excuse my possible naivete!

By the way, this is not homework help, although it seemed to fit appropriately under the homework-and-exercises tag--I would like an explanation of why the correct answer is in fact correct, not just the answer alone.

• I think more information is needed, string1 connects the $2$ kg box to what? what is the whole set up? where are the 2 boxes in the set up? A diagram would help. Commented Dec 9, 2015 at 5:07

I guess this is the scenario you are talking about:

Let's draw the free body diagram and apply 3rd law of motion:

I hope this answers your question. If you have any doubts, please feel free to comment and I will try my best to clear them.

• So would the answer be that it cannot be determined which is greater, but that they are definitely not equal? Commented Dec 9, 2015 at 12:11
• @Dopapp It cannot be determined unless the system is clearly described. Depending on the attachment of the strings and the blocks, the tensions will vary. Commented Dec 9, 2015 at 12:16