How to Avoid Common Mistakes in Solving Forces Problems?

[FaraDazed]

Homework Statement

A particles is under the influence of two forces, 500N at 50° from north and 350N at 350° from north. Find the magnitude and direction of the resultant pull on the particle.

Homework Equations

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The Attempt at a Solution

$x=500cos40-350cos80\\<br /> x=322.25N\\<br /> y=500sin40+350cos10\\<br /> y=666.08N \\<br /> <br /> \sqrt{322.25^2 + 666.08^2}=739.94N \\<br /> arctan(322.25/666.08)=25.82° from north. \\$
I am a bit confused on when to use cos or sin. The above is how a classmate pursaded me to change it to but on my first go I had
$x=500cos40-350sin10 \\<br /> <br /> y=500sin40+350cos10 \\$

 

[rude man]

Draw the vectors on an x-y plot (+y = North). It should be obvious from that.

 

[FaraDazed]

Draw the vectors on an x-y plot (+y = North). It should be obvious from that.

Thanks for your reply. I have already done that and the figure and direction obtained seem correct but I don't know for sure and if my method is correct.

EDIT: Sorry just realized my mistake. They are both the same but doing it a different way, my calculator was set on radians instead of degrees and that is why I was getting different figure to earlier sorry.

 

[Redbelly98]

..., my calculator was set on radians instead of degrees ...

A very common mistake. Remember to check the setting whenever you have an exam