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Question -

A plane is in level flight at constant speed and each of its twowings has an area of 25 m2. If the speed of the air is 180 km/h overthe lower wing and 234 km/h over the upper wing surface, determine the plane’smass. (Take air density to be 1 kg m–3).



Answer -

The area of the wings of the plane, A = 2 × 25 =50 m2

Speed of air over the lower wing, V1 =180 km/h = 50 m/s

Speed of air over the upper wing, V2 =234 km/h = 65 m/s

Density of air, ρ = 1 kg m–3

Pressure of air over the lower wing = P1

Pressure of air over the upper wing= P2

The upward force on the plane can be obtained using Bernoulli’sequation as:

The upward force (F) on the plane can be calculated as:

Using Newton’s force equation, we can obtain the mass (m)of the plane as:

4400 kg

Hence, the mass of the plane is about 4400 kg.

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