Final answer:
The acceleration of a 5-kg block being pulled by a net force is calculated by using Newton's second law of motion, resulting in an acceleration of 13.2 m/s².
Step-by-step explanation:
The acceleration of the 5-kg block can be calculated using Newton’s second law of motion, which states that the acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass. The net force can be calculated by subtracting the frictional force from the applied horizontal force. In this problem, we need to find the net force first: Net force = Applied force - Frictional force = 78 N - 12 N = 66 N. Then we use Newton's second law, which can be expressed as F = ma, with 'F' being the net force, 'm' is the mass, and 'a' is the acceleration.
To find the acceleration 'a', we rearrange the equation to a = F/m, and substitute the values calculated above: a = 66 N / 5 kg = 13.2 m/s². Therefore, the acceleration of the block is 13.2 m/s².