Question

In a test experiment on a model aeroplane in wind tunnel, the flow speeds on the upper and lower surfaces of the wings are 70 ms^–1 and 65 ms^–1 respectively. If the wing area is 2 m2 the lift of the wing is _______ N.
(Given density of air = 1.2 kg m^-3)

Answer 1

Correct Answer: 810

Step 1: Apply Bernoulli's Equation for Lift:

\( F = \frac{1}{2} \rho (v_1^2 - v_2^2)A \)

Where: \(\rho = 1.2 \, \text{kg/m}^3\), \(v_1 = 70 \, \text{m/s}\), \(v_2 = 65 \, \text{m/s}\), \(A = 2 \, \text{m}^2\)

Step 2: Compute Lift Force \(F\):

\( F = \frac{1}{2} \times 1.2 \times (70^2 - 65^2) \times 2 \)

Step 3: Simplify Calculation:

\( F = \frac{1}{2} \times 1.2 \times (4900 - 4225) \times 2 \)

\( F = \frac{1}{2} \times 1.2 \times 675 \times 2 \)

\( F = 810 \, \text{N} \)

Conclusion:

Therefore, the lift force is: \( F = 810 \, \text{N} \)