[العباس]

السلام عليكم


Answer: Here's the problem: the helicopter, before it even takes off, is traveling in an Easterly direction along with the rest of the earth as the Earth makes its daily rotation (in other words, the helicopter is said to already have an initial velocity in the horizontal direction). Thus, if one were to ascend straight up in a helicopter, one would just remain at rest relative to the ground below. The key point is that the helicopter, both before and after it takes off, already has the Earth's rotational speed in the easterly direction. To get to San Francisco, the helicopter must actually fly in a westerly direction with respect to the rotating earth.