For the situation shown in the figure below, the magnetic field changes with time according to the expression B = 2.07t^3 - 3.95t^2 + .808 and r2 = 2R = 4.96 cm. Figure: http://east.ilrn.com/books/sepsp06t/pse6e.31.32p.e.jpg (a) Calculate the magnitude of the force exerted on an electron located at point P2 when t = 1.92 s. (b) At what time is this force equal to zero? So, F = qvB and v = (qBr)/m, where m is the mass of an electron. I got the velocity formula by using F = ma, and substituting F as qvB and a with v^2/r. Then I solved for v. I used the two formulas to calculate the force, but is it incorrect. Am I doing this right or am I totally wrong? Any help would be great! Thx!!!