The blades of a windmill sweep out a circle of area :- Assume that the windmill converts 25% of the wind’s energy into electrical energy, and that A = `30 m^2, v = 36 km//h` and the density of air is `1.2 kg ,m^-3`. What is the electrical power produced ?

The blades of a windmill sweep out a circle of area :-What is the kinetic energy of the air ?

The blades of a windmill sweep out a circle of area:- If the wind flows at a velocity v perpendicular to the circle, what is the mass of the air passing through it in time t ?

The concentration of solution of sulphuric acid is 18M and has density 1.84gcm^-3 . What is the mole fraction and weight percentage of H_2SO_4 in the solution?

In a test experiment on a model aeroplane in a wind tunnel, the flow speeds on the upper and lower surfaces of the wing are 70 m s^-1 and 63 m s^-1 respectively. What is the lift on the wing if its area is 2.5 m^2 ? Take the density of air to be 1.3 kg m^-3

Estimate the average mass density of a sodium atom assuming its size to be about 2.5 overset@A . (Use the known values of Avogadro’s number and the atomic mass of sodium). Compare it with the density of sodium in its crystalline phase : 970 kg m^-3 . Are the two densities of the same order of magnitude ? If so, why ?

Two stones are thrown up simultaneously from the edge of a cliff 200 m high with initial speeds of 15 m s^-1 and 30 m s^-1 . Verify that the graph shown in Fig. 3.27 correctly represents the time variation of the relative position of the second stone with respect to the first. Neglect air resistance and assume that the stones do not rebound after hitting the ground. Take g = 10 m s^-2 . Give the equations for the linear and curved parts of the plot.

A transformer is working on 220V.50 Hz a.c. supply. The iron core of the transformer has a mass of 8.4 kg.. From the plot of B-H loop for the core, it is found that area of hte loop is 480 J m^-3 . If the density of iron is 7,500 kgm^-3 , find the loss of energy in the core of transformer in 1 hour.

Nazima is fly fishing in a stream. The tip of her fishing rod is 1.8 m above the surface of the water and the fly at the end of the string rests on the water 3.6 m away and 2.4 m from a point directly under the tip of the rod. Assuming that her string (from the tip of her rod to the fly) is taut, how much string does she have out ? If she pulls in the string at the rate of 5 cm per second, what will the horizontal distance of the fly from her after 12 seconds ? .

A steel wire of mass mu per unit length with a circular cross section has a radius of 0.1 cm. The wire is of length 10 m when measured lying horizontal, and hangs from a hook on the wall. A mass of 25 kg is hung from the free end of the wire. Assuming the wire to be uniform and lateral strains < < longitudinal strains, find the extension in the length of the wire. The density of steel is 7860 kg m^-3 (Young's modulues Y = 2 xx 10^11 N m^-2)