Physics: electromagnetism

1. When the direction of B is reversed, the direction of induced current in the moving rod is also reversed. This gives a magnetic force acting towards the left.

2. There won't be any induced current irrespective the coil is moving under acceleration or at constant speed. But there is induced emf on the coil, with side BC at higher potential than side AD.

3. Currents in X and Y are in the same direction, there is an attractive force produced between them. Such attractive force is thus from X to Y.

Currents in X and Z are in opposite dirctions, repulsive force is produced. The force on X is thus away from Z.

Hence, the resultant force is the vector sum of the forces from X to Y and away from Z, which gives a force in the direction shown by the arrow Q.

4. The induced current flows in the clockwise direction along the coil. As such, the current on the left hand side of the coil, which is in the magnetic field and flows upward, produces a magnetic force that acts towards the left.

The result is obvious by Lenz's Law. As the "change" that produces the induced current is the "motion towards the right", the induced current must a magnetic force to oppose the "change", i.e. a force towards the left.

The answer is option C.