In a graph of acceleration versus net force, the slope of the graph represents the inverse of the mass of the boat. This is because according to Newton's second law of motion (F = ma), rearranging the equation gives us acceleration (a) as a function of force (F) and mass (m): \( a = \frac{F}{m} \). Therefore, if you plot acceleration (a) on the y-axis and net force (F) on the x-axis, the slope of the line will be \( \frac{1}{m} \).
So, the correct answer is: the inverse of the mass of the boat.