Can you please help me on these questions below. can you guide me on what to do because i find them confusing.

Question

(a) In a wind tunnel, the flow speeds on upper and lower surface of a aeroplane wing are 70m/s and 63m/s. What is the lift on the wings going to be if its area is 2.5m². The density of air is 1.3kg m^-3.
Can you also explain me how you worked it out.

(b) I need to find the change in internal energy of a gas when it absorbs 100 calories of heat and performs work equal to 170 joules. I also need to find the change in internal energy of a gas when it absorbs 30 calories of heat and work equal to 65 joules is performed on it. Can you also explain me how you worked it out.

(c) A military helicopter transmits a long distance call. what range of frequency should it choose for that? If it receives a call at a frequency of 90MHz what should be the minimum size of antenna to receive the call. Can you also explain me how you worked it out.

thanks.

Answer 1

(a)
You need to use Bernoulli's equation for this:

p + 1/2*rho*V^2 = constant

where p is the static pressure, 1/2*rho*V^2 is the dynamic pressure, and their total is a constant. There is usually a gravity term (rho*g*h) in the equation, but it's negligible for air. This equation describes how a fluid with no work done on it has two pressure components that always add to the same thing. The more of the pressure is tied up in movement (dynamic pressure), the less pressure there is to exert forces on the wing.

Use this equation to calculate p on top of the wing, and p below the wing. Both equations will end up having a constant in them, but the net lift force on the wing is equal to the difference in the force on each side, so the constants will cancel no matter what value they have. You should find a difference of about 1210 pascals between the upper and lower surfaces, then multiply pressure * area to get force.

(b)
You need to use the first law of thermodynamics:

dU = dQ + dW

where dU is the change in internal energy, dQ is the heat added (positive means heat is going into the gas), and dW is the work done ON the system (positive is the work done on the system). Remember that work done ON a system is the same thing as negative work done BY a system, and vice-versa.

Just convert all the calorie values into joules: 1 calorie = 4.18400 joules. Then, keeping careful track of the signs, plug in values for dQ and dW to find dU.

(c)
An antenna should be as large as the wavelength of the waves it's collecting. You can find wavelength using this equation:
lambda = v / f
where lambda is the wavelength, v is the velocity, and f is the frequency.

90 MHz means a frequency of 90,000,000 cycles per second. Divide the velocity (which is the speed of light) by the frequency, and you'll have the wavelength.

Answer 2

are you cheating