Why the upper surface of wings of an aero plane are made convex upward and lower concave downwards ?

Why surface of tyres are made rough.

Why does a cloudily track from behind an aero plane flying at a great altitude?

The coefficient of friction between a body and the surface of inclined plane at 45^@ is 0.5. If g=9.8m/s^2 The acceleration of the body downwards in m/s^2 is

A pond is covered by a sheet of ice 2.0 cm thick (thermal conductivity 1.6 jm^(-1)s^(-1)k^(-1) . The temperature of the lower surface of ice is 0^@ C and that of the upper surface is -10^@ C . At what rate is heat conducted through each square meter of the ice ? What is the direction of this flow of energy ?