Acceleration vector exercise (coordinate system)

[sdadksajd]

Homework Statement

Please read the attachment =)

All the formulas I was given are also on a separate attachment

I initially thought the answer was the last one because I did rf-ri and subtracted across and got 0 mi + 25mj but I am not sure =[

Homework Statement

 

[PeterO]

Homework Statement

Please read the attachment =)

All the formulas I was given are also on a separate attachment

I initially thought the answer was the last one because I did rf-ri and subtracted across and got 0 mi + 25mj but I am not sure =[

Homework Statement

rf-ri sounds like a good idea, but 0 mi + 25mj isn't the answer to that.

ri has a 50mi term
rf has a -50mi term

so when you subtract them the answer will not be zero [since they are different]

 

[sdadksajd]

Oh thanks for the much needed advice. I redid the problem and got the first choice as my answer which was from subtracting -25 from 25 and 125 from 100. Can anyone verify that choice a is correct =[]

 

[PeterO]

Oh thanks for the much needed advice. I redid the problem and got the first choice as my answer which was from subtracting -25 from 25 and 125 from 100. Can anyone verify that choice a is correct =[]

My previous post should have said 25mi and -25mi - you can't look at "pictures" and respond at the same time.

While the first option is correct - the description of what you did is all backwards.

You actually subtracted 25 from -25, and subtracted 100 from 125.

 

[sdadksajd]

Thanks a ton peter I understand now :)

 

[PeterO]

Oh thanks for the much needed advice. I redid the problem and got the first choice as my answer which was from subtracting -25 from 25 and 125 from 100. Can anyone verify that choice a is correct =[]

By the way: applying the logic of multiple choice questions leads you to this answer.

If you consider just the i components.

If you add them [or subtract poorly], you get 0i [only one option has this].

If you subtract the second from the first you get 50i [only one option has this]

If you subtract the first from the second you get -50i [two options have this]

If the answer was not one of the -50i ... examples, you would not even have to consider the j component - possible but unlikely.

consider the j component. when you subtract here, you either get 25j or -25j

only one of those possibilities is offered - and there is your answer!

Playing the multiple choice game rather than understanding the problem is not a recommended technique - but if all else has failed it is useful.
Remember: with a normal problem you are trying to find the answer; with a multiple choice question you are only trying to identify which of the options is the answer.