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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?

What are your thoughts?

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


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?
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
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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