1. The problem statement, all variables and given/known data We take a horizontal copper bar with length of 20cm and attach it from the middle to a vertical spring which mass is neglected and has a spring constant K, we apply a horizontal magnetic field with magnitude 1/2 T and have a 10A current run in the copper bar. The bar rests after the spring is stretched by 10cm of its original length before turning on the current. 1 Define the forces affecting the system at rest knowing that the electromagnetic force is downards 2. Find K. 2. Relevant equations 3. The attempt at a solution I honestly have no idea what to do, the wording is somewhat confusing, here's how I ran the problem in my mind: When we attach the bar to the spring, it stretches by length X0=m*g/k, and the system is at rest. I don't know what x0 is. The forces affecting the system then are Fs0 and Fs0' which cancel out, plus W (weight) and R (normal force) which also cancel out. Is this correct? When we turn on the current, the electromagnetic force keeps pulling the body down, and the restoring force keeps trying to bring it up, thus, they also cancel out along the other forces. The forces affecting the system now are F(electromagnetic), F(Restoring force), W (Weight), R(Normal force), Fs0 and Fs'0. Is this correct? So I have 2 rest points, one before the current, and one after the current? How am I supposed to find K? If I say that F(electromagnetic) = F (Restoring force) and then plugin the values: I*L*B*= -*K*X 10*2*10^-1*1/2=-K*X 1 = -K*X K=-1/X K=-1/-10^-1 = 10 N.m^-1 This doesn't really sound correct to me, is it?