Current Events > weekly "wtf am I doing wrong in math class" topic

(+) Yeah! (+)

Have something moving 500 meters per second at an angle of 160 degrees, a force moving at 20 meters per second with an angle of 85 degrees (relative to the original center point) starts acting on the object.

What's the resulting vector?

I used the law of cosines and ... nothing. I'm assuming that the 85 degrees is the actual new angle. Been crunching numbers for over an hour now and it's driving me crazy lmao

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I feel like the system is broken, I've tried every possible logical problem solving technique here -_-

Wait wtf

I used Law of Cosine to calculate the speed of the new vector, and it tells me that speed is wrong. Yet I calculated the angle of the new vector using that speed and got the right number. How the hell does that make sense??

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I thought this was gonna be another one of those "@ MATH PEOPLE" topics, but then I remembered that that guy has me blocked.

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UnholyMudcrab posted...

I thought this was gonna be another one of those "@ MATH PEOPLE" topics, but then I remembered that that guy has me blocked.

Oh that is shitty man who would block you??

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I don't remember vector math, don't you just draw the triangle? That should be simple...

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ChocoboMogALT posted...

I don't remember vector math, don't you just draw the triangle? That should be simple...

That's literally it. It's a triangle.

I have the square root of 500^2+20^2-2(20)(500)cos(85) and that's somehow wrong.

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welp
Just did the following and final problem in less than two minutes... still can't finish this one though.

I hate the technical side of this course sometimes -_-

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Sorry I'm not home to write this out right now. Are you measuring the angle from inside the triangle?

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I thought vectors broke down into horizontal and vertical, then you summed them?

Ruvan22 posted...

I thought vectors broke down into horizontal and vertical, then you summed them?

So, I have one vector going at 160 meters. The second vector's tail end goes from the head of the first vector at an angle of 85 degrees, and then it connects to the to the tail of the first vector to form a triangle.

so I assumed at that point you could just treat it like a regular triangle :\

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You should do this by its components. If you actually draw the triangle you'll see that you need to do a lot of extra work to figure out the interior angles. You're trying to use angles from the problem and those aren't the ones in the final triangle.

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Frostshock posted...

You should do this by its components. If you actually draw the triangle you'll see that you need to do a lot of extra work to figure out the interior angles. You're trying to use angles from the problem and those aren't the ones in the final triangle.

I feel like the 85 degree angle is from the final triangle, no?

Also not sure how to figure out the components since I don't know the radius or anything like that.

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Well no, the problem is telling you the starting vectors are 160 and 85 degrees. It doesn't say anything about what happens when you combine them, that's your job.



You can either figure out the properties of the triangle formed by these (annoying) or break the vectors into their components (easy).

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The funny thing is it already combines it for me on the assignment.

I am gonna head out to bed in a minute, but I appreciate you taking the time to draw those up - because it *was* combined already I didn't think to just analyze it as two separate items like that.

Once I get the components I imagine it's just a matter of figuring the difference and calling it good?

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Update: tried the vector addition method aaaaaaand

still not accepting my answer :( Thankfully I started this early, asked about it on my class discussion board for the week and someone else responded they were also struggling with this problem specifically.... starting to think it's a technical issue with the software.

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yo this is driving me crazy

I found a tool online where you can enter two vectors and it calculates the resulting vector

the system didn't accept that answer either

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If you type in the exact question through Google, it's possible to find a web link on it or close to something similar.

Steffenfield posted...

If you type in the exact question through Google, it's possible to find a web link on it or close to something similar.

I have done that, and I have followed the steps exactly (in fact the sites I've found talk about the Law of Cosines).

There's that stupid Chegg site that has the solution to this specific problem but you have to pay for that and I'm not about to pay for something like this, especially not when I've been able to figure everything else out (especially with folks' help here in the past).

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I'd do this by splitting both vectors into two components (one being x cos(angle) and the other being x sin(angle)) and doing it from there

But forces and velocities aren't comparable, you'd need to calculate acceleration from the force and use that to calculate the speed

This is just a weird problem tbh. I'm about to go to bed, I'll check back in the morning. If you ever have similar "maths of motion" problems feel free to @ me, I TAed this stuff for two years^^

Edit: I misread, it's two velocities. Yeah, split both into two components (so that you have two sets of components that point in the same directions) and add them together. If you're still stuck I can draw it and see what I get but not until Thursday I'm afraid, I have a all-day university thing tomorrow :/
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Yeah, most times Chegg will find it but only for a price. :/

I just found this https://www.nicolet.k12.wi.us/faculty/dgibbon/vector%20apps%20worksheets%20answers.pdf

and followed the steps

and still... nothing.

I'm tempted to just roll through like 480 - 550 one at a time to see what happens.

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Oh wait I copied down the wrong number somehow when I broke it down into components... FINALLY got the right darned answer.

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Ask your instructor for help?

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skermac posted...

Ask your instructor for help?

I did reach out on the class' discussion post for this section, only got one response from a student commiserating with me lol.

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You aren't even telling us the answers you inputted except that one time and that answer was obviously wrong to me. I got 505.5 angle 157.8 as the approximate resultant vector for the record.

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Hexenherz posted...

Oh wait I copied down the wrong number somehow when I broke it down into components... FINALLY got the right darned answer.

What was the answer?

Paragon21XX posted...

You aren't even telling us the answers you inputted except that one time and that answer was obviously wrong to me. I got 505.5 angle 157.8 as the approximate resultant vector for the record.

Me too, using the law of cosines but 105 as the angle instead of 85 like TC had in the original post

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