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# Newtons laws and Helicopters watch

1. Kinda stuck on this question if anyone cares to help. Its question 1B

http://www.ocr.org.uk/download/pp_11...n_gce_g484.pdf
2. It states that the air is in the shape of a cylinder of radius 5m.
i) The volume of air will be the volume of the cylinder. (You must know the formula).
Mass of air = density x volume.
For the length of the cylinder; the length of the column of air created in 5 seconds at a speed of 12 m/s is....?
ii) momentum = mv
iii) force is change of momentum per second
iv) this force must balance the weight of the 'copter
3. (Original post by Stonebridge)
It states that the air is in the shape of a cylinder of radius 5m.
i) The volume of air will be the volume of the cylinder. (You must know the formula).
Mass of air = density x volume.
For the length of the cylinder; the length of the column of air created in 5 seconds at a speed of 12 m/s is....?
ii) momentum = mv
iii) force is change of momentum per second
iv) this force must balance the weight of the 'copter
Thanks very much, I did understand it was a column of air and was using volume formula but I was confused about how to find out height. simple things like displacement=Vt are the things I sometimes forget
4. When they ask you to calculate the change in momentum of a car during a impact, why is it we cannot just work out the P(before) and P(after) and take it away to get the correct answer?
5. (Original post by Jetblast)
When they ask you to calculate the change in momentum of a car during a impact, why is it we cannot just work out the P(before) and P(after) and take it away to get the correct answer?
Well, change in momentum is momentum after minus momentum before, so you will need to give more information about why this is not allowed.
If two cars are in collision, although individually their momentum will change, the total momentum (sum of both cars) remains constant.

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