1. Two tractor trailers, each 12 m long and 4.0 m tall, are parked next to each
ID: 1480191 • Letter: 1
Question
1. Two tractor trailers, each 12 m long and 4.0 m tall, are parked next to each other as shown in (Figure 1) . A light wind that is blowing at 5.0 m/s in the parking lot but at20 m/s between the trailers causes the air pressure between them to drop.
What is the magnitude of the force exerted by the air on each trailer? (Use 1.0 kg/m3 for the air mass density.)
F =
2. The air in a room held at a steady temperature T is made up largely of nitrogen molecules(mN2 = 4.652 × 1026 kg) and oxygen molecules(mO2 = 5.3135 × 1026 kg). Even though both gases are diatomic, assume they behave as monatomic gases.
At equilibrium, what is the ratio of the average speed of the nitrogen molecules to the average speed of the oxygen molecules?
vN2/vO2 =Explanation / Answer
1)
Area of tractor= 4m*12m=48m^2
F=A*change in pressure
use Bernoullis equation:
P1-P2=1/2rho(v2^2-v1^2)
change in P= 1/2(1.0kg/m^3)(20^2-5^2)
change in P= 187.5
F=187.5*48m^2
=9000 N
2) VN2 = sqrt(3*KB*T/m) m is the molecular mass of the gas in kilo grams
then VN2 = sqrt(3*kB*T/m1)
VO2 = sqrt(3*kB*T/m2)
VN2/VO2 = sqrt(m2/m1) = sqrt[(5.3135*10^-26)/(4.652*10^-26)] = 1.068
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