Three forces act on a moving object

  • #1

Homework Statement



Three forces act on a moving object. One force has a magnitude of 80.0 N and is directed due north. Another force has a magnitude of 60.0 N and is directed due west. What must be the magnitude and direction of the third force, such that the object continues to move with a constant velocity?

Force 1 = 80.0 N due north.
Force 2 = 60.0 N due west.

Homework Equations



a^2 + b^2 = c^2
Theta = tan^-1(fy/fx)


The Attempt at a Solution



First I started by plotting the problem on a cartesian plane. I then took my known quantities of 80.0 N due north (along the positive y axis) and 60.0 N due west (along the negative x axis) and used pythag to find the net force, the answer of which was 100 N.

I then attempted to find the direction using Theta = tan^-1(fy/fx) = tan^-1(80/60) = 53.13.

My question is, am I right in assuming that I must counteract the first two forces with the third to ensure a constant velocity? If so I would appreciate any help in this regard.
 

Answers and Replies

  • #2
lewando
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Careful with your direction. 53.13 degrees with respect to what? West of North? North of West? Otherwise, your assumption is correct.
 
  • #3
Careful with your direction. 53.13 degrees with respect to what? West of North? North of West? Otherwise, your assumption is correct.

Thanks. I will be sure to always define that in future :smile:

So the next step in my problem having confirmed my original assumption (thanks again) would be to determine the magnitude of the third force and it's direction:

The net force I worked out to be 100 N and the direction to be 53.13 degrees North of West :smile:

So the magnitude would have to be 100 N in the opposite direction being 53.13 degrees South of East?

I appreciate all help as I have just begun studying again and I want to fully grasp each concept as I go along.

Thanks.
 
  • #4
lewando
Homework Helper
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So the magnitude would have to be 100 N in the opposite direction being 53.13 degrees South of East?

Yep.:approve:
 

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