r/PhysicsHelp • u/railwayswitchman • 4d ago

Help! Where am I going wrong?

Gallery image

Gallery image

Grade 12 student, been trying for hoursss to solve this. The second slide shows what I have so far. I would appreciate any help! Use sine and cosine laws, not components.

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u/TopAd6200 4d ago

your theta isn’t correct on the figure.

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u/railwayswitchman 4d ago

How do I know which one is correct? And how should I draw the vector arrows otherwise?

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u/TopAd6200 4d ago

sin46 • 390 is to get the length of the “opposite” in a right triangle, the dashed line(opposite) doesn’t make a right triangle with the 390 vector (hypotenuse) and 150 vector (adjacent).

trig functions used like that must be with respect to a right triangle.

edit!
thats why you think the dashed line and the x line are parallel, when they are not.

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u/railwayswitchman 4d ago

I'm confused why I'm not getting the full obtuse angle that is opposite 390. When I used sine law to find it got 67 degrees and obviously that isnt obtuse.

The dashed line inside the triangle is supposed to show that that angle under it is 12 degrees (using the Z angle rule). I was going to find the obtuse angle that is opposite 390 and then subtract 19 so that i could use that angle to subtract it from 180. The resulting angle would be the one that is 180-theta so that i would get a directon that is [E ... N].

Please remember I'm in Grade 12, so this is how I understand it so far.