An electron of mass moving with velocity in the vicinity of the North Pole experiences a force
where is a constant and the position vector of the particle is with respect to an origin located at the North Pole. Write down the equation of motion of the electron, neglecting gravity. By taking the dot product of the equation with show that the speed of the electron is constant. By taking the cross product of the equation with show that
where is a constant vector. By taking the dot product of this equation with , show that the electron moves on a cone centred on the North Pole.