BR Physics Fluids and Solids examples

[Natnow]

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I have a couple of questions I need help with (from BR Physics Fluids and Solids review) please!

If you could also provide me with an explanation that would be awesome!

Ex. 7.7b While you are stopped at an intersection turn lane, a large truck zooms by, just a few feet from your car. As the truck passes, your car will be:
A. pulled towards the truck, because the increased wind speed between the truck and the car lowers the pressure there.
B. pushed away from the truck, because the increased wind speed between the truck and the car lowers the pressure there.
C. pulled towards the truck, because the increased wind speed between the truck and the car increases the pressure there.
D. pushed away from the truck, because the increased wind speed between the truck and the car increases the pressure there.

Ex 7.6b The plunger of a hypodermic syringe has a cross-sectional area of approximately 0.5cm^2, where the attaching needle has cross-sectional area of 0.005cm^2. If a doctor pushes in the plunger at a speed of 0.3 cm/s, what is the flow sped of the medicine through the needle?
A. 0.003cm/s
B. 30cm/s
C. 300cm/s
D 3000cm/s

 

[Natnow]

Ex 7.8b
Which of the following will increase the possibility of turbulent air flow around the winds of an airborne plane?
A. Flying at faster speeds and using larger wings
B. Flying at slower speeds and using larger wings
C. Flying at faster speeds and using smaller wings
D. Flying at slower speeds and using smaller wings

I feel that flying at a faster speed will increase turbulent air flow, from Reynolds number equation but don't know how to think through the rest of the problem.

 

[Sed8&Intub8]

I have a couple of questions I need help with (from BR Physics Fluids and Solids review) please!

If you could also provide me with an explanation that would be awesome!

Ex. 7.7b While you are stopped at an intersection turn lane, a large truck zooms by, just a few feet from your car. As the truck passes, your car will be:
A. pulled towards the truck, because the increased wind speed between the truck and the car lowers the pressure there.
B. pushed away from the truck, because the increased wind speed between the truck and the car lowers the pressure there.
C. pulled towards the truck, because the increased wind speed between the truck and the car increases the pressure there.
D. pushed away from the truck, because the increased wind speed between the truck and the car increases the pressure there.

Ex 7.6b The plunger of a hypodermic syringe has a cross-sectional area of approximately 0.5cm^2, where the attaching needle has cross-sectional area of 0.005cm^2. If a doctor pushes in the plunger at a speed of 0.3 cm/s, what is the flow sped of the medicine through the needle?
A. 0.003cm/s
B. 30cm/s
C. 300cm/s
D 3000cm/s

7.7 should be A. The way I think about it is when the truck passes by you it pushes the air away (increased wind speed) from that area creating low pressure, the air will rush from everywhere towards that area of low pressure, so as the air is coming towards that area to fill that area it will also push your car towards that area (and leaves and dust and grass)

7.6 should be B. Flow rate is constant. AV=AV. (0.5)(0.3) = (0.005)(x). Solve for x

 

[Sed8&Intub8]

Ex 7.8b
Which of the following will increase the possibility of turbulent air flow around the winds of an airborne plane?
A. Flying at faster speeds and using larger wings
B. Flying at slower speeds and using larger wings
C. Flying at faster speeds and using smaller wings
D. Flying at slower speeds and using smaller wings

I feel that flying at a faster speed will increase turbulent air flow, from Reynolds number equation but don't know how to think through the rest of the problem.

Well if you have a larger wing wouldn't there be more chance of having turbulent air flow? You have more area for it to occur in. The is an R in the equation it is for radius, essentially the size of the wing can substitute for it.