Could someone please help me with these physics questions? A quick explanation is only needed with the answer as I do not want you to spend to much time

(3) (10 pts.) A thin, 50.0-cm-long metal bar with mass 750 g rests on, but is not attached to, two metallic supports in a uniform 0.450 T magnetic field, as shown in the figure. Note gravity is pulling down on the rod. A battery and a 25.0 0 resistor in series are connected to the supports. What is the highest voltage the battery can have without breaking the circuit at the supports? R + M B X XXXX XXX(4) (10 pts.) A particle with charge 6.98 x 10- C is moving in a region where there is a uniform 0.810 T magnetic field in the +x-direction. At a particular instant, the velocity of the particle has components Vr = -1.71 x 10* m/s, Vy = 2.98 x 104 m/s and vz = 5.12 x 104 m/s. What are the components of the force on the particle at this time