Why there two propellers in a helicopter ?

Assertion : There are two propellers in a helicopter. Reason : Angular momentum is conserved.

A helicopter is flying along the curve y=x^(2)+2 . A soldier is placed at the point (3, 2). Find the nearest distance between the solider and the helicopter.

A helicopter lifts a body of mass 100kg to a height of 500m at a constant speed. It takes 5min to lift the body. Find the work done by the helicopter and the power required.

Give reason for the following (a) Bicycle wheels are provided with spokes (b) There are two fan a helicopter.

Statements: All gliders are parachutes. No parachute is an airplane All airplanes are helicopters. Conclusions: I. No glider is an airplane II. All gliders being helicopters is a possibility.

The helicopter has a mass m and maintains its height by imparting a downward momentum to a column of air defined by the slipstream boundary as shown in figure. The propeller blades can project a downward air speed v, where the pressure in the stram below the blades is atmospheric and the radius of the circular cross section of the slipstream is r. Neglect any rotational energy of the air, the temperature rise due to air friction and any change in air density rho . If the power is doubled, the acceleration of the helicopter is :-

A helicopter is flying horizontally at 8m//s at an altitude 180m when a package fo emergency medical supplies is ejected horizontally backward with a speed fo 12m//s relative to the helicopter. Ignoring air resistance what is horizontal distance between the package and the helicopter when the package hits the ground?