Final answer:
A rock thrown at 8 km/s without air resistance would continue moving away from Earth, as this speed exceeds Earth's escape velocity. For a rock thrown at 15.0 m/s from a bridge 20.0 m high, it will hit the water at 24.8 m/s due to energy conservation. The final speed is independent of the throwing direction, due to the transformation of potential energy to kinetic energy.
Step-by-step explanation:
When a rock is thrown with an initial speed fast enough, such as 8 km/s, and we neglect air resistance, the motion of the rock can be analyzed using the principles of physics, specifically energy conservation. Assuming we are discussing Earth, 8 km/s is above Earth's escape velocity, which means the rock would not fall back down and would instead continue moving away from Earth. However, if we were considering throwing a rock from a bridge 20.0 m above water at 15.0 m/s, energy conservation says that regardless of the direction thrown, when it strikes the water, it will do so at a certain speed determined by the initial kinetic energy and the potential energy related to the height. The potential energy at the height of the bridge is transformed into kinetic energy as the rock falls. The speed of the rock when it hits the water would be found by considering both the potential energy lost and the initial kinetic energy it had. Happens refers to the outcome or result, and when it's used in physics, it often relates to an event or process such as the motion of the rock. The speed of 24.8 m/s for the rock thrown from the bridge is calculated using the principles of energy conservation, which will apply to the rock thrown at 8 km/s under the idealized condition of having no air resistance.