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Can anyone help provide an explanation?

  • Thread starter gunblaze
  • Start date
Qn1: When paddling a canoe, one can attain critical speed with relatively little effort, but to go faster beyond this critical speed requires more effort. Why?

Qn2: Why do jet planes usually fly at altitudes above 10000m although it takes a lot of fuel to climb to that height?

Thx..
 
2,208
1
What are your thoughts?

Hint: Friction
 
yup.. around there. Friction and the drag force
 
but how..? when u fly higher, u get lesser friction..?
 
V

vsage

Right. I may have the number wrong but when flying at the altitudes planes do on long flights (around 30,000 feet) the air is about 20% as thick as it is at sea level.
 
u mean air is less dense at high altitudes, therefore, by using F=pAv^2, we get a lesser drag force?
 
2,208
1
Yeah, the air density is much less up there. This also affects the plane's lift though.

Can you think of anything for the canoe?
 
no.. that's really what i don't know
 
2,208
1
Look at the force equation you gave above for drag resistance. Although that is the application for air, it is a simliar principle for fluids. What do you notice as velocity increases?
 
oOO.. I see. so as the speed of the canoe increases, the larger the drag force is on the canoe.

Whao, thx guys!
 

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