Final answer:
The primary force responsible for a cyclist's acceleration during the initial 3-5 seconds of pedaling in a sprint on a flat surface is the applied force (C).
Step-by-step explanation:
The primary force responsible for a cyclist's acceleration during the initial 3-5 seconds of pedaling in a sprint on a flat surface is the applied force (C).
When a cyclist pushes down on the pedals, they apply a force to the bicycle. This applied force is what propels the cyclist forward and causes their acceleration.
Other forces such as friction and gravitational force play a role in cycling, but the primary force responsible for acceleration in this scenario is the applied force.