When a nonzero net force acts on an object the force

A.changes the motion of the object
B.Must be greater than the reaction force
C.Does not change the motion of the object
D.is equal to the weight of the object

Imagine a football stationary on the ground or even moving through the air.

You then apply a nonzero force (i.e. you kick it)

What happens?

F = m a =change of momentum/change in time

so
it accelerates, changes velocity

Is a nonzero net force an unbalanced force?

Afraid not, try again.

You can't have a force greater than the reaction force as Newtons 3rd Law states that 'Every action has an equal and opposite reaction'.

Imagine kicking a wall. If you kick it gently your foot doesn't feel much of a force back but if you kick it hard you will hurt your foot. The reaction force depends on the force you apply in the first place.

edit: my reply before was to your reply of 'B'?

A nonzero force just means a force. It means that 0N isn't allowed as that wont affect anything.

It's not D either I'm afraid.
Damon said the correct answer there.

The correct answer is A: changes the motion of the object.

To understand this, let's first clarify the concept of net force. Net force is the vector sum of all the individual forces acting on an object. When there is a nonzero net force acting on an object, it means that the total force acting on the object is not zero.

According to Newton's second law of motion, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The equation for this relationship is F = ma, where F represents the net force, m represents the mass of the object, and a represents the acceleration.

If a nonzero net force acts on an object, it means that there is an unbalanced force acting on it, causing a change in its motion. The object will accelerate in the direction of the net force. The greater the net force, the greater the acceleration will be. Therefore, the force changes the motion of the object.

Option B, "Must be greater than the reaction force," is not necessarily true. The reaction force, also known as the opposing force, is the force exerted on an object in the opposite direction. It is equal in magnitude but opposite in direction to the force exerted by the object. The net force is the result of the combination of all forces acting on an object, including both the applied force and any opposing forces.

Option C, "Does not change the motion of the object," is incorrect, as explained above. A nonzero net force always causes a change in the object's motion.

Option D, "Is equal to the weight of the object," is also incorrect. The weight of an object is the force of gravity acting on it and is given by the equation W = mg, where W represents the weight, m represents the mass of the object, and g represents the acceleration due to gravity. The weight of an object is generally not equal to the net force acting on it, unless the object is in equilibrium (meaning all forces acting on it cancel each other out, resulting in a net force of zero).