# Thread: Need help with angles

1. ## Need help with angles

Two equal forces act on an object at 80 degree to on another. the resultant force has a magnitude of 100 N. What are the forces.
This is what I did

not sure what to do after

2. Originally Posted by supersaiyan
Two equal forces act on an object at 80 degree to on another. the resultant force has a magnitude of 100 N. What are the forces.
This is what I did

not sure what to do after
Use the Cosine rule to calculate the equal forces:

Let f denote the magnitude of the forces. Then solve for f:

$100^2=f^2+f^2-2\cdot f \cdot f \cdot \cos(100^\circ)$

I've got $f \approx 65.27\ N$

3. Originally Posted by earboth
Use the Cosine rule to calculate the equal forces:

Let f denote the magnitude of the forces. Then solve for f:

$100^2=f^2+f^2-2\cdot f \cdot f \cdot \cos(100^\circ)$

I've got $f \approx 65.27\ N$
Thanks, I got the same thing

4. Sorry, I got one more question

$|\overrightarrow{u}|=110, |\overrightarrow{v}|=75$ and the angle between $\overrightarrow{u}$ and $\overrightarrow{v}$ (when placed tail to tail) is $100^\circ$. Find $|\overrightarrow{u} + 3\overrightarrow{v}|$

5. Originally Posted by supersaiyan
Sorry, I got one more question

$|\overrightarrow{u}|=110, |\overrightarrow{v}|=75$ and the angle between $\overrightarrow{u}$ and $\overrightarrow{v}$ (when placed tail to tail) is $100^\circ$. Find $|\overrightarrow{u} + 3\overrightarrow{v}|$
1. If you have a new question start a new thread. Otherwise you risk that nobody will notice your need for help.

2. Use the Cosine rule:

$l = \sqrt{110^2+(3 \cdot 75)^2-2\cdot 110 \cdot 3 \cdot 75 \cdot \cos(100^\circ)}$

I've got $l \approx 261.6$