Investigating Net Force in Two Dimensions

[alexandria]

Homework Statement

Homework Equations

no equations required

The Attempt at a Solution

i already answered the question, but i just want to know if i wrote the right direction for the Fnet.
is it [N 10 W] or [W 10 N]?[/B]

this is how i wrote it:
Fnet: 1165 N [N 10 degrees W]

 

[haruspex]

this is how i wrote it:
Fnet: 1165 N [N 10 degrees W]

As I explained in another thread, N 10 degrees W would mean 10 degrees W of North. Is that what it looks like in your diagram?
Also, you don't show how you got 10 degrees. It is correct, to that many digits. Can you quote one more digit?

 

[alexandria]

ok this is how i got 10 degrees and the Fnet:

Step #1: Use the cosine law to solve for the magnitude of the net force

c2 = a2 + b2 – 2abcosC

c2 = (800 N)2 + (400 N)2 – 2(800 N)(400 N)cos150 degrees

c = 1165 NStep #2: Use the sine law to solve for the angle of the net force

SinB/b = SinC/c

SinB/400 N = Sin150 degrees/1165 N

b = sin-1 (400 N x Sin150o/1165 N)

b = 9.8 » 10 degrees

To determine the angle for the net force, subtract 20 fromb, as this results in the angle needed to describe the direction of the net force.

20 degrees – 10 degrees = 10 degrees

Fnet = 1165 N [N 10 degrees W] it can also be looked at as 10.2 degrees, i just rounded 9.8 to 10 exactly.

The net force on the log is 1165 N at an angle of 10 degrees west of north.

 

[alexandria]

in this case, the 800 N vector is further to the north and the resultant (Fnet) is further to the west.
i described the angle between them by saying [N ... W]

so is this correct?

 

[haruspex]

it can also be looked at as 10.2 degrees, i just rounded 9.8 to 10 exactly.

Yes, that's fine.

the 800 N vector is further to the north and the resultant (Fnet) is further to the west.
i described the angle between them by saying [N ... W]

This is the identical mistake you are making on the other thread. When stating the direction of the resultant, we no longer care about any of the directions of the contributing forces. We must quote the direction relative to the standard compass points.

 

[alexandria]

ok so in this example taken from my lesson, the 1.0 N vector is directed East, and the Fnet is further north, to describe the direction, they said the Fnet was E...N
can't this method be applied to my problem as well?

 

[alexandria]

[N 10 degrees W] is meant to indicate the direction in reference to the log's original position.
if this is not correct, should it be [W 10 degrees N]?

I was reading another forum with the same problem:
https://www.physicsforums.com/threads/net-force-in-two-dimensions.727612/