Hello:
I remembered yesterday an issue I have discussed intensely in the past but never solved to my complete satisfaction. Maybe someone here can help.
I would like to know how the following statement is to be read:
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“An airplane cannot take off from a runway which is moving backwards (like a treadmill)
at a speed equal to its normal ground speed during takeoff.â€
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1) An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to the airplane's normal ground speed during takeoff.
2) An airplane cannot take off at a speed equal to its normal ground speed during takeoff from a runway which is moving backwards (like a treadmill).
3) An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to the runway's normal ground speed during takeoff of any airplane.
I see the following differences:
1) The runway is moving backwards at a certain speed (equal to the airplane's normal ground speed) and the airplane cannot take off.
2) The runway is moving backwards (at any speed) and the airplane cannot take of at its normal ground speed.
3) The airplane cannot take off and the runway is moving backwards at a speed of zero since the runway's normal ground speed is zero.
Can the statement be read either way and be grammatically correct? Personally, I feel version 3 is grammatically the most correct version even though it is most contrary to what I assume is the writer's intention. Is there another possible version (even if it does not make sense physically) that is correct? Are multiple versions possible and acceptable grammatically? My spellchecker suggests that a comma is missing after the “which†or that the word “which†is replaced with “thatâ€. I feel cannot change the spelling of the sentence though. I would like to know how the current version is to be understood however clumsily it was written.
I have some opinions in regard to the technical issue involved. In my opinion, discussing or trying to solve this engineering challenge needs to happen after it is clear how the challenge is to be understood as it was written.
Welcome to the forum Karsten.
First, like many other test questions I've seen, even on the SAT, this is a poorly written question. I taught science for 30 years, wrote test questions for ACT, and have a background in physics, so I'm pretty sure I can help you out here. The main problem with that question is the ambiguity of the word "its." Depending on whether "it" is the plane or the runway, the interpretation would be different. Also, the question is what I'd call a run-on sentence. Finally, it appears to be intended as a "true or false" question, which are rarely pedagogically useful.
However, since the ground speed of a normal runway is zero, I think I see the question-writer's intent. I think that would be your version 1. If I rewrote that question, it would read like this:
An airplane's normal take-off speed is 100 mph. The airplane is placed on a runway that is moving backward like a treadmill at 100 mph. If the airplane is moving forward with a speed of 100 mph relative to the treadmill surface, will it be able to take off?
Now the situation is clear. Ambiguity is removed, and the answer should be apparent. That answer is clearly "NO." The airplane needs an airspeed of 100 mph to take off. A wheel-based speedometer would read 100 mph in the situation described, but an airspeed indicator (based on a pitot tube) would read zero.
Interesting. You accept that it is valid to have to guess in regard to the intent of the writer of the question. I struggle with this although I accept that it sometimes seems necessary. No language is perfect. I agree that my version 1 is probably the version most likely to be intended by the writers of the original statement. I think it is really not written to say that.
I think we both suspect that the treadmill is supposed to move backwards at the speed equal to the normal ground speed of the plane. But that would then not require that the airplane is required to take off at it normal ground speed. And if one accepts that the airplane is supposed to take off at its normal ground speed, the descriptor for any particular speed of the backwards moving runway falls away. The way it is written, "its" cannot describe the speed of the airplane AND the conveyor.
I agree this is a poorly written statement and that it hinges around the "its". I have also requested clarification regarding the definition of "ground speed" and received no answer. I can only assume that they mean it to be the speed of the airplane relative to the surface it sits on (as in measured by how fast the wheels turn while it is on the ground).
While I accept that the airplane will take off without great difficulties, it will not take off at its normal ground speed. Those little wheels will be spinning awfully fast until the plane gets airborne.
What is the best interpretation of the original statement if one DOES NOT try to interpret what the writers wanted to ask?
Your last sentence contradicts itself.
Ooops
OK.
How does one need to read the original statement without trying to guess what they wanted to say?