Newton's second law of motion states that in an inertial frame of reference the net force acting on an object is equal to the mass m of the object multiplied by its acceleration :
and are vectors and the mass m is a scalar that we assume to be constant. We also assume that the net force and the acceleration are in the horizontal direction x.
We are told that |F| = 170 N and that m = 300 kg. So we get that:
Provided the scream is a constant pitch at the source, Doppler effect will make the pitch increase as the velocity of the source towards the listener increases.
I think the correct answer would be that because electromagnets are powerful and can be turned off and on anytime. Electromagnet is a magnet in which the magnetic field is made by the electric current that is induced to the system.