A scale model of a sports car is tested in a wind tunnel
PHYSICS · Subjective · CBSE · Physics · Units and Measurements · Units and Measurements
Problem
A 1:8 scale model of a sports car is tested in a wind tunnel. The tunnel air has the same density as atmospheric air. At a test speed of 40m s−1 the drag force recorded on the model is 18N. For pressure drag the force is known to depend only on air density ρ, a characteristic frontal area A, and the square of the speed v.
(i) Determine the ratio of the frontal area of the prototype to that of the model.
(ii) Assuming dynamic similarity so that the dimensionless drag coefficient is unchanged, calculate the drag force that would act on the full-size car moving at the same speed of 40m s−1 on a level road.
(iii) A road test of the actual car measures a drag of 1.30kN at 40m s−1. Compute the percentage difference between the wind-tunnel prediction and the road-test value, and suggest one possible reason for the discrepancy.