The friends observed that as the mass and speed increased, the radius of the circular path increased, and as the charge magnitude and field strength increased, the radius decreased. In fact, the radius is directly proportional to the mass and speed, and inversely proportional to the charge magnitude and magnetic field strength. Safiya asks Amy how she can derive this relationship. Which response is correct? "Because the velocity and magnetic field are at right angles, FB = qv B , and because the motion is uniformly circular, the magnetic force is also equal to mass times centripetal acceleration, m v2 r . Set these two expressions equal and solve for r." "Because the velocity and magnetic field are at right angles, FB = qvB, and because the motion is uniformly circular, the magnetic force is also equal to mass times centripetal acceleration, m v r . Set these two expressions equal and solve for r." "Because the velocity and magnetic field are at right angles, FB = Bv q , and because the motion is uniformly circular, the magnetic force is also equal to mass times centripetal acceleration, m v2 r . Set these two expressions equal and solve for