The working of magnetic braking of trains is based on

A bar magnet is allowed to fall vertically through a copper coil placed in a horizontal plane. The magnet falls with a net acceleration, is

A jet plane of wing span 20 m is travelling towards west at a speed of $400 \mathrm{~ms}^{-1}$. If the earth's total magnetic field is $4 \times 10^{-4} \mathrm{~T}$ and the dip angle is $30^{\circ}$, at that place, then the voltage differences developed across the ends of the wing is