suppose that you measure the length of a spaceship, at rest relative to you, to be 400 m. how long will you measure it to be if it flies past you at a speed of u=0.75c

Along wire carrying a 4.2 a current perpendicular to the xy-plane intersects the x-axis at x=−1.7cm. a second, parallel wire carrying a 3.0 a current intersects the x-axis at x=+1.7cm. part a at what point on the x-axis is the magnetic field zero if the two currents are in the same direction? express your answer to two significant figures and include the appropriate units.