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XJS
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Hi all! I have been accepted by a university and have been given the second round interview question.
However, I am pretty stumped as to how to answer it. Here's the question:
Please answer the following question. Your answer should be handwritten on no more than three (3) sides of A4 paper. Note this is an open-ended question: there is no ‘right answer’! You are free to make any assumption you feel is necessary. Your existing mathematics and physics knowledge will be sufficient to answer this question, but you may need to apply your knowledge in an unfamiliar way.
If a sheet of paper were dropped from a helicopter hovering at a height of 1000 m, (i) with what force would it hit the ground? (ii) how long would it take to reach the ground? (iii) would your answer be different if the helicopter were moving?
For this question I want to find out:
1) Downwards force of paper
2) Downdraft of helicopter (caused by lift) onto the paper)
3) Reynolds number of air column from ground to helicopter to find out if airflow is turbulent or laminar (I'm not even sure if airflow has turbulent or laminar properties. I only learned that for fluid within pipes)
4) How do I calculate reynolds number if I don't know the cross-sectional velocity?
5) Upwards resistance of air (Terminal velocity. I really don't know how to calculate this part)
6) At which point will the paper reach terminal velocity (so I know the time and the distance), then subtract that distance from 1km to find out the remaining time it takes for the paper to hit the ground.
Point 6 continued) Essentially, I will need t [tv] (time to to terminal velocity) + t [tvg] (time it takes to reach ground after achieving terminal velocity)
Anyone have any ideas? Thank you !
However, I am pretty stumped as to how to answer it. Here's the question:
Please answer the following question. Your answer should be handwritten on no more than three (3) sides of A4 paper. Note this is an open-ended question: there is no ‘right answer’! You are free to make any assumption you feel is necessary. Your existing mathematics and physics knowledge will be sufficient to answer this question, but you may need to apply your knowledge in an unfamiliar way.
If a sheet of paper were dropped from a helicopter hovering at a height of 1000 m, (i) with what force would it hit the ground? (ii) how long would it take to reach the ground? (iii) would your answer be different if the helicopter were moving?
For this question I want to find out:
1) Downwards force of paper
2) Downdraft of helicopter (caused by lift) onto the paper)
3) Reynolds number of air column from ground to helicopter to find out if airflow is turbulent or laminar (I'm not even sure if airflow has turbulent or laminar properties. I only learned that for fluid within pipes)
4) How do I calculate reynolds number if I don't know the cross-sectional velocity?
5) Upwards resistance of air (Terminal velocity. I really don't know how to calculate this part)
6) At which point will the paper reach terminal velocity (so I know the time and the distance), then subtract that distance from 1km to find out the remaining time it takes for the paper to hit the ground.
Point 6 continued) Essentially, I will need t [tv] (time to to terminal velocity) + t [tvg] (time it takes to reach ground after achieving terminal velocity)
Anyone have any ideas? Thank you !
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