My TAs pointed out to me a common misconception about situations where multiple forces act on an object. Many students appear to think that in such a case the net force must be equal to 0 N. This is in general not true. You need to keep in mind that the net force acting on an object is equal to ma. This tells you: 1. If you know that object is not moving or moving with constant velocity, its acceleration is 0 m/s^2 and the net force is 0 N. 2. If you know the object is moving, but you do not know its acceleration, then you cannot assume that the net force is 0 N. If the acceleration is non zero, the net force will be non zero. Please make sure you understand this, especially for Exam #1. Frank Wolfs _____________________________________________________________________ Frank L. H. Wolfs e-mail: wolfs@pas.rochester.edu Department of Physics and Astronomy University of Rochester B&L 203A, RC Box 270171 fax: (585) 275 - 8527 284 Hutchison Rd. phone: (585) 210 - 3271 Rochester, NY 14627 http://teacher.pas.rochester.edu/