Question about Resultant Forces

[Pablo1122]

Alright, so after looking at this video to do it



I did the following.

F1(65N) = 65cos(30)i+65sin30i

Then using the radian circle I saw that 30* has x,y coordinates of sqrt3/2 and 1/2 respectively. So as shown in the video I did

65(root3/2)i+65(1/2)j

= 56.3i + 32.5j

I did this for the left one too (30N).

But for the one at the bottom (20N) I get the degree of it to be 250. (270-20) = 250.

250* is not on the radian circle so how can I write 250* in terms of x,y coordinates?

Thanks in advance.

 

[BvU]

Hello Pablo,

Please post in the homework forum (and make good use of the template there!)

180-20 = 250 seems strange to me. But 270 - 20 - 250 and that's the right angle. Why do you say it's not on the radian circle ? Does that go from $-\pi$ to $+ \pi$ ? If so, how far from 0 to 270 when starting at 0 ?

 

[Pablo1122]

Hello Pablo,

Please post in the homework forum (and make good use of the template there!)

180-20 = 250 seems strange to me. But 270 - 20 - 250 and that's the right angle. Why do you say it's not on the radian circle ? Does that go from $-\pi$ to $+ \pi$ ? If so, how far from 0 to 270 when starting at 0 ?

Oh you I wrote it wrong, I meant to write 270-20 = 250.

But if we look at this radian circle. We see that 240* = (-1/2, -sqrt3/2) and then it goes to 270* = (0,-1). How can I find the x,y coordinates for 250* and use it in the equation?

And sorry about posting in the wrong section, I'll fix it next time. Do I need to repost this to the homework section or is it fine?

 

[BvU]

I see. 250 degrees isn't in the list. Calculators (or spreadsheets) not allowed ? You need $\ \cos 250^\circ\$ and $\ \sin 250^\circ$

Thread will be moved by a moderator, don't worry.

 

[Pablo1122]

I see. 250 degrees isn't in the list. Calculators (or spreadsheets) not allowed ? You need $\ \cos 250^\circ\$ and $\ \sin 250^\circ$

Thread will be moved by a moderator, don't worry.

Oh my bad I posted it over there already. I 'll see if I can delete it.

Ya we can use calculators but maybe I am doing it wrong. Should it be in degrees or radians?

I see. 250 degrees isn't in the list. Calculators (or spreadsheets) not allowed ? You need $\ \cos 250^\circ\$ and $\ \sin 250^\circ$

Thread will be moved by a moderator, don't worry.

Ooh, I can just do it on my calculator? I assumed you'd have to use the radian circle. Well... I feel dumb. Thanks a lot though :)

And I already posted it to the homework section again but I'll post that it's been solved. Thanks again.

 

[BvU]

When in radians mode your angle is $250^\circ \displaystyle {\pi\over 180^\circ}$

-- lots of people blindly type in an angle in the wrong mode and end up with nonsense (and marks lost), so be warned.