A motorboat is cruising on a calm lake. A velocity-time graph showing its motion is presented below.

![Velocity-time graph for a motorboat on a lake. The vertical axis represents Velocity in m/s (from 0 to 15) and the horizontal axis represents Time in s (from 0 to 250). The graph has four distinct sections:

• Section A: from 0 to 40 seconds, accelerating uniformly from 0 to 12 m/s.
• Section B: from 40 to 120 seconds, maintaining a constant velocity of 12 m/s.
• Section C: from 120 to 180 seconds, decelerating uniformly from 12 m/s to 0 m/s.
• Section D: from 180 to 240 seconds, remaining stationary at a constant velocity of 0 m/s.](https://assets.mathsgenie.co.uk/aqa-qb/7e516225-7b19-48cb-8a41-5969c75ccf45.png)

In two sections of the graph, the horizontal forces acting on the motorboat are balanced.