An object is being acted upon by three forces and as a result moves with a constant velocity. One force is 60.0 N along the +x -axis, and the second is 75.0 N along the +y -axis. What is the magnitude of the third force?
A) 48.0 N
B) 15.0 N
C) 67.5 N
D) 135 N
E) 96.0 N

Question

An object is being acted upon by three forces and as a result moves with a constant velocity. One force is  60.0 N  along the  +x -axis, and the second is  75.0 N along the  +y -axis. What is the magnitude of the third force?
A)  48.0 N
B)  15.0 N
C)  67.5 N
D)  135 N
E)  96.0 N

Quizplus · Accepted Answer

Since the object moves with a constant velocity, the net force acting on it must be zero (Newton's first law). The third force must therefore be equal in magnitude and opposite in direction to the resultant of the first two forces. The resultant force can be found using the Pythagorean theorem, as the forces on the x and y axes are perpendicular to each other: $\sqrt{60^2 + 75^2} = \sqrt{3600 + 5625} = \sqrt{9225} = 96.0 N$. Thus, the magnitude of the third force must be 96.0 N to balance the other two forces.

An Object Is Being Acted Upon by Three Forces and as a Result