A simple force resolving question... answer doesn't seem to make sense (1 Viewer)

[emilios]

http://imgur.com/bVdNTz9

The answer says F/N = tan(theta) but I keep getting cot(theta)

When I resolve the triangle in the bottom left and use Newton's 3rd Law I get Fsin(theta) = mg and by a similar process, Ncos(theta) = mg. So then my expression for F/N is cot(theta)...

The answer just says "Resolving the forces at...". I really don't like this topic because all they seem to say is "just resolve the forces".

 

[braintic]

That's not right.

You should get:
Fsin(theta)+Ncos(theta)=mg
and
Fcos(theta)-Nsin(theta)=0

But it is easier to resolve forces in the normal and tangential directions.
You then get:
N=mgcos(theta)
and
F=mgsin(theta)
which gives the correct answer

 

[Kurosaki]

http://imgur.com/bVdNTz9

The answer says F/N = tan(theta) but I keep getting cot(theta)

When I resolve the triangle in the bottom left and use Newton's 3rd Law I get Fsin(theta) = mg and by a similar process, Ncos(theta) = mg. So then my expression for F/N is cot(theta)...

The answer just says "Resolving the forces at...". I really don't like this topic because all they seem to say is "just resolve the forces".

I got , did you resolve the weight force correctly? When you resolve the weight force, you should let the component perpendicular to the plane equal N, and let the one parallel to it equal to F, and put negative signs in front of them (opposite directions).
this is due to Newton's first law, which says if you are stationary/moving at constant velocity, the net force is 0.
Doing that, you should get

, and .....I think.