Final answer:
A net force must be acting on an object of mass m moving on a horizontal surface with an increasing velocity, as per Newton's second law of motion. This force leads to the acceleration of the object in the direction of the net force. The magnitude of the net force can be determined by using the mass of the object and its acceleration.
Step-by-step explanation:
If an object of mass m is traveling on a horizontal surface and its velocity is increasing at a constant rate, we can confidently assert that option b) A net force is acting on the object is correct. According to Newton's second law of motion, acceleration occurs when a net force acts upon an object. Since the question specifies a constant increase in velocity. or acceleration, it directly implies there is a net force acting in the direction of the object's motion.
This is akin to the concept presented in Newton's second law, which states that the rate of change of momentum of an object is directly proportional to the net external force applied. Thus, for the object to be accelerating, a force must be continuously applied to it. For example, if we push a sled along a smooth icy surface, it will only continue to accelerate as long as we are applying a force. Once we stop pushing, the acceleration stops as well, although the sled maintains its last velocity (assuming zero friction).
In the context of the normal force, when an object is at rest, the magnitude of the normal force acting on it is equal to its weight and acts in the upward direction while the weight or gravitational force acts downward. The symbol N = mg represents the normal force where g is the acceleration due to gravity. This is directly related to the questions surrounding the forces in play when an object is stationary or moving with different velocities.