Final answer:
A sled pulled with constant velocity experiences zero acceleration because there is no change in its speed or direction, which are the conditions for acceleration.
Step-by-step explanation:
When a father pulls his daughter on a sled with a constant velocity, the correct answer is A) Zero acceleration. Acceleration is defined as the rate of change of velocity. If the velocity is constant, this means there is no change in speed or direction, and therefore, the acceleration is zero. This concept can be further understood by examining three ways in which an object can accelerate: by speeding up, slowing down, or changing direction.
Referring to the examples provided, it's clear that constant velocity implies neither the magnitude nor the direction of velocity is changing. If we compare a vehicle moving with a constant speed in a straight line and one that begins to increase speed, the latter is the one undergoing acceleration. Therefore, for an object moving at constant velocity, like the sled in the question, there is no change in kinetic energy associated with acceleration, hence no acceleration is occurring.