PLEASE HELP ME , it’s my exam

In a series circuit the __ is the same at every point

In which of these cases are the two wave points considered to be in phase with each other?

1. explain how you calculate the net force in any direction on the box. 2. suppose an upward force of 15n is added to the box. what will be the net vertical force on the box? 3. what force could be applied to the box to make the net force in the horizontal direction zero? explain. 4. suppose a force of 25n to the right is added to the box. what will be the net force to the right?