Final answer:
The situation in which friction can cause an increase in velocity is when a box is sitting on a flatbed truck as it accelerates forward; friction prevents the box from sliding and increases its velocity along with the truck.
Step-by-step explanation:
Friction is commonly known to act opposite to the direction of motion, thereby slowing down the velocity of moving objects. However, the question at hand asks for an example where friction might actually cause an increase in velocity. Considering the options given:
- Air flow over an airplane wing is not friction, but an example of aerodynamic lift.
- A golf ball rolling downhill on a putting green is an example where friction acts to decrease the ball's velocity.
- A box sitting on a flatbed truck as the truck accelerates forward would experience friction that could lead to an increase in the box's velocity if the friction prevents the box from sliding backward as the truck moves forward.
- The fan on an airboat does not involve friction causing an increase in velocity; instead, it's a form of propulsion.
The correct answer is: c) A box sitting on a flatbed truck as the truck accelerates forward. This is because the friction between the box and the flatbed provides the necessary force to increase the velocity of the box as the truck starts to move forward.