http://www.geocities.com/bridgestein/Bffield.jpg (copy and paste the above address to your browser please) In fact I know the answers of this problem, but I have a question. Here's the question. A charge +q moving with constant velocity v enters into a uniform magnetic field region as shown. The magnetic flux density is B. a) What is the direction of the force F experienced by q? b) What is the work done by F? c) What kind of motion it is performing? d) Express the radius of curvature r of the change in terms of B, v, m and q. Where m is the mass of the charge. ans: a) Direction of force is always perpendicular to the direction of q. The point charge will go upward. From the part (d), I know it is performing circular motion and that the work done by F is 0 J! d) r = mv/(Bq) Why it is performing circular motion? Can't it be an elliptical motion?