- #1

Arman777

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## Homework Statement

Calculate the ratio of the drag force on a jet flying at ##1200 km/h## at an atttude of ##15 km## to the drag force on a prop-driven transport flying at half that speed and altitude.The density of air is ##0.38(\frac {kg} {m^3})## at ##10 km## and ##0.67(\frac {kg} {m^3})## at ##5 km##.Assume that the air-planes have the same effective cross-sectonal area and drag coefficient C

## Homework Equations

##F_D=\frac 1 2CAρv^2##

## The Attempt at a Solution

Here C and A are the same so ## F_D## jet will be ##F_1## and ##F_D## plane will be ##F_2##

##F_1=ρ_1(v_1)^2## and ##F_2=ρ_2(v_2)^2##

The question ask ratio so we dont care about units ( I guess )

##ρ_1## which at 15 km is I found approximately ##0.235 (\frac {kg} {m^3})## ( from Inverse ratio )

##ρ_2## which at 7.5 km is I found ##0.525 (\frac {kg} {m^3})##

So ##\frac {F_1} {F_2}=4 \frac {0.235} {0.525}=1.79##

answer is 3.3

I dont know where I went wrong

Thank you