Uniform circular motion problem

[J-dizzal]

F_T is the net force right? The magnitude of F_T is not 559.98.

Also there are 2 angles against the vertical. The problem may want you to find the smaller of the two angles.

i guess i found it.

 

[J-dizzal]

F_T is the net force right? The magnitude of F_T is not 559.98.

Also there are 2 angles against the vertical. The problem may want you to find the smaller of the two angles.

thanks again Nathanael!

 

[Nathanael]

No problem. I was going to tell you about the arctan method after you found it your way. The arctan method was the first that came to my mind.
(But the arccos(a.b/(|a||b|)) method is also a very good one to know! It's far more general.)

 

[J-dizzal]

i really need to work on recognizing what is the logical next step to take with what information i have. i spend way too much time on a single problem

 

[J-dizzal]

No problem. I was going to tell you about the arctan method after you found it your way. The arctan method was the first that came to my mind.
(But the arccos(a.b/(|a||b|)) method is also a very good one to know! It's far more general.)

did you find the angle with the arccos method? what values did you use for a and b? i could only get 180degs

 

[Nathanael]

i really need to work on recognizing what is the logical next step to take with what information i have. i spend way too much time on a single problem

It comes with practice. I hope at least that you feel you are getting better and better (even if slowly).

did you find the angle with the arccos method? what values did you use for a and b? i could only get 180degs

I didn't use that method, but it would work. You had the dot product right (62\hat i-mg\hat j)\cdot(0\hat i+\hat j)=-mg but then you are supposed to divide by \sqrt{(mg)^2+62^2}*1 but for some reason you were dividing by mg. That's why in post #30 I said the magnitude of the net force is not mg.

I think it was just a careless mistake, just got to take things slow.

 

[J-dizzal]

It comes with practice. I hope at least that you feel you are getting better and better (even if slowly).I didn't use that method, but it would work. You had the dot product right (62\hat i-mg\hat j)\cdot(0\hat i+\hat j)=-mg but then you are supposed to divide by \sqrt{(mg)^2+62^2}*1 but for some reason you were dividing by mg. That's why in post #30 I said the magnitude of the net force is not mg.

I think it was just a careless mistake, just got to take things slow.

yep i sure did miss that, thanks for point it out to me though.

 

[J-dizzal]

ill be on tomorrow with some statics problems, most likely. hope youre on to help. goodnight. thanks again.

 

[Simon Bridge]

The general method to add vectors in physics is called "heat to tail".
http://www.physicsclassroom.com/class/vectors/Lesson-1/Vector-Addition
... to find angles in a triangle you should use trigonometry.

Once the vectors are sketched out - everything else should be clear.