Pulley and wheel and axle

What is the principle used in wheel and axle? Mention its applications.

The radius of the wheel of a wheel and axle is 4 times the radius of the axle. What is the mechanical advantage of the wheel and axle?

Two wheel and axle systems P and Q are connected as shown in the figure. The radii of wheels and axles of P and Q are 20 cm, 27 cm, 3 cm and 5 cm, respectively. If L = 540 kgwt, find E.

The radii of the axle and the wheel are increased by 3 times and 5 times, respectively. The new M.A. advantage of the wheel and axle is

State one way in which the friction between wheel and its axle can be reduced.

Figure-2.85 shows a block B of mass m, cart C of mass M, and the coefficient of static between the block and the cart is mu . Neglect frictional between wheels and axles and the rotational effects of the wheels. Determine the minimum value of F which must be applied on B such that it will not slide. [(mg)/(mu)(1+(m)/(M))]

How is a screwdriver an example of a wheel-and-axle?