Final answer:
The net force provided by the water that stops a swimmer is buoyancy, which effectively counteracts the swimmer's weight and any initial momentum. When completely submerged, this buoyant force, along with water friction, is sufficient to bring the swimmer to a halt.
Step-by-step explanation:
The net force exerted by the water on a swimmer who comes to a stop 2.0m below the surface is primarily buoyancy. Buoyancy is the upward force exerted by a fluid that opposes the weight of an object immersed in it. When evaluating forces acting on a swimmer who has entered the water after jumping from a diving board, we must consider both gravity and buoyant forces. While gravity pulls the swimmer downward, buoyancy pushes them up. The swimmer stops because the upward buoyant force balances out the swimmer's weight and any additional forces, such as the momentum from the jump and the viscosity of the water, which could be described as a form of friction.
For a swimmer with a mass of 80.0 kg who has just jumped from a board 10.0 m above the water, the swimmer's weight would contribute to a downward gravitational force. However, to come to a stop within the water, the upward buoyant force must be significant to counteract this, along with the initial momentum the swimmer had on entering the water. If the swimmer comes to a stop within 3 seconds, the average buoyant force can be calculated based on the change in momentum over that time period.