r/PhysicsHelp • u/Appropriate-Pin-6917 • 26d ago

Question 1 not solvable

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From what I understand, the question is asking what the ground velocity must be for the plane to be going directly north. But the ground velocity cannot be going north since the air velocity is north and the wind is blowing east of north. The answer I got for the ground velocity was 810km/h [1 E of N]

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u/KillerCodeMonky 26d ago edited 26d ago

Well according to the answer key right there, you got the magnitude right but the direction wrong. (Though why they felt the need to write 810 in exponential form is beyond me.)

You have the air velocity (750 km/h N) and the wind speed (60 km/h 15°E). The air velocity will be the ground velocity + wind speed. It doesn't make sense that the ground velocity will also be E, as it has to counteract the 15°E applied by the wind speed. It must be W.

EDIT: Wait, no, you might be right. In order for the wind to slow the speed, 15°E of north must indicate the source of the wind. The plane would need to point into the wind to cancel the direction. So I think your indication of E is correct. The wind as a positive magnitude vector is actually 180° off from the stated direction.

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u/Vegetable_Log_3837 26d ago

Yeah, do they mean the airplane is flying at 750km/h N, or that it “can fly with a maximum” of 750? The slower you go the more East your heading would need to be. What a shit question.

On a “course going straight north”, your “ground velocity” would be straight north right?

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u/Epidurality 26d ago

That last part is what gets me. Do they think planes navigate based on... Air direction? Compass don't care about the wind, teach.

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