# Thread: Need to understand how they solved this problem

1. ## Need to understand how they solved this problem

Below is the answer to a problem. I cannot figure out how they did it I tried to start with the math but hit a dead end.

Any help would be great:

I am unable to figure out how they did the following problem, I see where they substitute in for ay, and I am fine there.

I dont understand the steps they took to get the answer below:

I tried the following:

After this point I kept running into some walls I tried factoring out a negative, and I tried a few other things but I am not doing something right as its not coming up like it should so I must be missing a rule or not using it correctly.

thanks,

Brian

2. Originally Posted by wilder7bc
Below is the answer to a problem. I cannot figure out how they did it I tried to start with the math but hit a dead end.

Any help would be great:

I am unable to figure out how they did the following problem, I see where they substitute in for ay, and I am fine there.

I dont understand the steps they took to get the answer below:

I tried the following:

After this point I kept running into some walls I tried factoring out a negative, and I tried a few other things but I am not doing something right as its not coming up like it should so I must be missing a rule or not using it correctly.

thanks,

Brian
Hi Brian,

Solving, we get

$m_1\left(g+\frac{m_2-m_1}{m_1+m_2}g\right)=m_1\left(\frac{g(m_1+m_2)+g( m_2-m_1)}{m_1+m_2}\right)$

$=m_1\left(\frac{2gm_2}{m_1+m_2}\right)$

3. Originally Posted by Archie Meade
Hi Brian,

Solving, we get

$m_1\left(g+\frac{m_2-m_1}{m_1+m_2}g\right)=m_1\left(\frac{g(m_1+m_2)+g( m_2-m_1)}{m_1+m_2}\right)$

$=m_1\left(\frac{2gm_2}{m_1+m_2}\right)$

Well my physics book gave me the answer as this:

The book states the answer is:

I dont understand how they got to that answer or the math and rules involved.

The answer your giving me is not the same as the book does. I dont really need the answer as I have it already from the book.

I need to know how the book came to get their final answer.

Thanks for assisting, but I am just after the rules and math that they used to get their answer.

If you could show me that would be awesome as I am trying to move onto the next problem but I am one of those people who obsess when I dont understand something and its so hard for me to move on to the next physics problem as I have problems letting go lol

Thanks,

Brian

4. Yes, just multiply my last step out,

$m_1\left(\frac{2gm_2}{m_1+m_2}\right)=\frac{m_1}{1 }\ \frac{2gm_2}{m_1+m_2}=\frac{2gm_1m_2}{m_1+m_2}$

$=\left(\frac{2m_1m_2}{m_1+m_2}\right)g$

5. Originally Posted by Archie Meade
Yes, just multiply my last step out,

$m_1\left(\frac{2gm_2}{m_1+m_2}\right)=\frac{m_1}{1 }\ \frac{2gm_2}{m_1+m_2}=\frac{2gm_1m_2}{m_1+m_2}$

$=\left(\frac{2m_1m_2}{m_1+m_2}\right)g$
Awesome thanks!

Brian

6. ## oh wow

I just went back and looked at that and I missed that entire thing because I didnt finish out my math. I was so busy looking for some difficult rule that I missed addition of fraction and multiplying it out to finish up.

Brian

7. Originally Posted by wilder7bc
Below is the answer to a problem. I cannot figure out how they did it I tried to start with the math but hit a dead end.

Any help would be great:

I am unable to figure out how they did the following problem, I see where they substitute in for ay, and I am fine there.

I dont understand the steps they took to get the answer below:

I tried the following:

After this point I kept running into some walls I tried factoring out a negative, and I tried a few other things but I am not doing something right as its not coming up like it should so I must be missing a rule or not using it correctly.

thanks,

Brian
Post the whole problem to make our life easier.

8. Oops.
I did not see the other replies
Sorry :O