4. The extension of a circular bar tapering uniformly from diameter d1 at one end to diameter d2 at the other end, and subjected to an axial pull of P is __________ the extension of a circular bar of diameter d1d2 subjected to the same load P.
8. The efficiency of jet propulsion for a ship with inlet orifices at right angles to the direction of motion of ship, will be maximum when the relative velocity of the jet and ship is equal to twice the velocity of the ship.