Final answer:
The net force acting on a 2.0 kg rock thrown upward at any point in its flight, including the top, is the gravitational force, which is calculated as the product of the rock's mass and the acceleration due to gravity. For a 2.0 kg rock, this force is 19.6 newtons downward.
Step-by-step explanation:
A rock is thrown straight up into the air with a speed of 30m/s. What is the net force acting on the rock? To answer this, we need to consider the only force acting on the rock during its entire trajectory, which is gravity. Since we are ignoring air resistance, the net force on the rock at any point, including the top of its trajectory, is the gravitational force (F₂).
The gravitational force can be calculated using Newton's second law, F = ma, where m is the mass of the object and a is the acceleration due to gravity (on Earth this is approximately 9.8 m/s²).
Therefore, the net force acting on the rock, which is also the weight of the rock, is given by (net force) = (mass) × (acceleration due to gravity). With a mass of 2.0 kg, the net force acting on the rock is: F₂ = (2.0 kg) × (9.8 m/s²) = 19.6 N.