Question

In: Physics

A Freight truck is driving down I-95 at 70 mph. a. Assuming the truck is driving...

A Freight truck is driving down I-95 at 70 mph.

a. Assuming the truck is driving through calm air, what is the pressure that is exerted on its frontal area when cruising at that speed? Make necessary simplifying assumptions.

b. How many pounds of force are experienced by the front of the truck assuming its frontal area is flat and 13 ft by 8 ft?

c. In full-scale wind tunnels, engineers recreate wind flow in driving conditions to understand how their designs would fare in the real world. What wind speeds are typically reached in wind tunnels? Cite your sources.

d. What power from the truck’s motor is needed to overcome this force?

Extra credit: What is the ultimate thermodynamic effect of propelling the truck for one mile over level terrain?

Solutions

Expert Solution

(C)full scale wind tunnle cross section area is 166 square meter and inside the tunnel there are two fans,runs by 4000 hourse power electric meter.so inside the wind tunnel wind speed is 53 m/s.informtain can be obtain at nasa website.

(D)inside the wind tunnel air pressure = air density × velocity^2

1.225×(53)^2=3441 pascal

So force= pressure×area=3441×9.6=33034 newtons or 33 kilo newton approx

Power= force × distance/time=force×velocity

As wind is alredy applying enough pressure on truck.we make calculation on the basis if truck is moving at a speed of 30 m/s then power needed in this condition

33034×30=991020 newton meter/second

1 newton meter/second=0.00134 hp so 991020nm/s=991020×0.00134=1328hp approx


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