College Physics 10th Edition by Raymond Serway,Chris Vuille

Exercise 36

A 1.00-kg ball having net charge Q = 5.00 C is thrown out of a window horizontally at a speed v = 20.0 m/s. The window is at a height h = 20.0 m above the ground. A uniform horizontal magnetic field of magnitude B = 0.010 0 T is perpendicular to the plane of the ball's trajectory. Find the magnitude of the magnetic force acting on the ball just before it hits the ground. Hint: Ignore magnetic forces in finding the ball's final velocity.