Final answer:
The force on the student's foot when they dropped a 25 lb weight does not simply equal the weight, as impact forces depend on factors like velocity, collision duration, and the area of impact. Option D is correct.
Step-by-step explanation:
When a student dropped a 25 lb weight on his foot, the force exerted on the foot upon impact does not simply equal the weight of the object because forces during impact are influenced by factors such as the velocity of the weight upon impact, the duration of the collision, and the properties of the surfaces involved. The gravitational force acting on the object is the weight, which is the force due to gravity.
Newton's second law explains that the net force on an object causes acceleration. In the case of a falling object where air resistance is negligible, this force is the gravitational force. However, during impact, the force experienced by the student's foot would also depend on how the weight is distributed over time and the area of impact, not just the weight itself.
This is because the force at the moment of impact involves the deceleration of the weight and the duration of the impact, which typically occurs over a very short time, resulting in a higher force than just the weight.