Three forces act on a moving object

[theniknakman]

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.

 

[lewando]

Careful with your direction. 53.13 degrees with respect to what? West of North? North of West? Otherwise, your assumption is correct.

 

[theniknakman]

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

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

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.

 

[lewando]

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

Yep.

 

[rwisz]

I would first make sure to clarify the terms "constant velocity" and "counteract." "Constant velocity" means that the object is moving at a steady speed in a straight line, without any change in direction. "Counteract" could mean that the third force must be equal in magnitude and opposite in direction to the net force, thus resulting in a zero net force and constant velocity. However, it could also mean that the third force must be directed in a specific way to balance out the other two forces and maintain constant velocity.

Assuming that the third force must be equal in magnitude and opposite in direction to the net force, then your calculations are correct. The third force must have a magnitude of 100 N and be directed due south (180 degrees from due north) to counteract the 80 N due north and 60 N due west forces.

If the third force must be directed in a specific way to balance out the other two forces, then we would need more information about the object's initial velocity and the direction of its motion. Without this information, it is not possible to provide a specific answer.

In general, as a scientist, it is important to clarify any ambiguous terms and make sure that all necessary information is provided in a problem before attempting to solve it. This ensures that our solutions are accurate and meaningful.