A square coil, with side I=20 cm and resistance R=0.1 , moves on horizontal plane with constant velocity v=2m/s along the axis . The cool is immersed in a magnetic field orthogonal to the plane of the coil and varying in space as B = B₀+ ax (a=T/m).

neglecting the self -inductance, calculate the force necessary to keep the moving coil in uniform motion.