Final answer:
The net force on a rock thrown vertically into the air at its highest point is its weight, which is the result of the gravitational force pulling it downwards. This force is equivalent to the mass of the rock multiplied by the gravitational acceleration.
Step-by-step explanation:
When a rock is thrown vertically into the air and reaches its highest point, the net force on it is equivalent to the gravitational force pulling the rock downwards. Even when the rock is at its peak and appears to be stationary for a moment, gravity is still acting on it. Therefore, the net force is not zero; it is actually equal to the weight of the rock, which is the mass of the rock multiplied by the gravitational acceleration (approximately 9.8 m/s2 on Earth).
For example, if a 2kg rock is thrown upwards, at the highest point, the net force acting on the rock is F = m*g, where m is the mass and g is the acceleration due to gravity. So F = 2kg * 9.8m/s2 = 19.6N downwards.
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