Chang sees the following formula on a website about newton’s second law. what does the symbol f in the formula indicate that chang needs to do? a. he needs to find the net force acting on the object in a direction. b. he needs to use only forces acting in the direction of motion. c. he needs to combine the horizontal and vertical forces. d. he needs to multiply the horizontal and vertical forces.

This question is based on the fundamental principle of  laws of motion.

Before going to describe Newton's second law, first we fave to understand Newton's first law.As per Newton's first law it is impossible to change the state of rest or of uniform motion of an object along straight line unless and until it is compelled by external unbalanced force. It indicates that when there is a net or unbalanced force acts on  the body,it will undergo motion.. Balanced forces have no role in changing the state of motion or rest of the body.

Now we have to understand newton's second law. It states that the rate of change of momentum is directly proportional to the  applied force and takes place along the direction of force. Mathematically it is given by-

Here p is the momentum and t is the time.

The symbol F in the above equation stands for the net force not on force only.It is so because the momentum of a body will change when there will be a net force acting on it.All the forces acting on the body can cot contribute to the motion.Some forces may cancel each other.Only the unbalanced or net force can do so.

Hence option  A is right.