A conducting rod of mass 50 g and length 10 cm can slide without friction on two long, horizontal rails. A uniform magnetic field of magnitude 5 mT exists in the region as shown. A source S is used to maintain a constant current 2 A through the rod. If motion of the rod starts from the rest, its speed after 10 s from the start of the motion will be

• A

  2 cm/s

• B

  8 cm/s

• C

  12 cm/s

• D

  20 cm/s