The blades of windmill sweep out a circle of area A.
(i) 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?
(ii) What is the kinetic energy of the air?
(iii) Assume that the windmill converts 25% of the wind's energy v=36km/h and density of the air is 1.2 kg m. What is the el;ectrical power produced?

Under the correct alternative.
Whan a conservation force does positive work on a body, the potential energy of the body increase decrease/remains unaltered.

Work done by a body against friction always results in a loss of its kinetic/potential energy

The rate of change of total momentum of a many particle systems is proportional to the external force/sum of the internal forces on the system.

A body of mass 3 kg is under a constant force, which causes a displacement S in metre in it, given by the relation S = \(\frac{1}{3}\) t₂, where t is in an second. Find the work done by the force in 2s.

A family uses 8 kW of power. (a) Direct solar energy is incident on the horizontal surface at an average rate of 200 W per square meter. If 20% of this energy can be converted to useful electrical energy, how large an area is needed to supply 8 kW? (b) Compare this area to that of the roof of a typical house.

When a 300 g mass is hung from a vertical spring, it stretches from equilibrium by 10 cm.What work is required to stretch it by next 5 cm?

Two identical ball bearings in contact with each other and resting on a frictionless table are hit head-on by another ball bearing of the same mass moving initially with a speed v. If the collision is elastic, which of the following (figure) is a possible result after collision?

Draw a graph showing variation of potential energy, kinetic energy and the total energy of a body freely falling on Earth from a height h.

A body of mass 2kg is initially at rest. A constant force of 5 N acts on it for 10s. Calculate the average power of the force.

A ball bounces to 80% of its original height. What fraction of its mechanical energy is lost in each bounce?

An electric fan of mass 2 kg falls from the ceiling of a lift moving down with uniform speed of 2 ms^-1. It hits the floor of the lift (length of the lift = 2m) and does not rebound. How much heat will be produced by the impact?

A block of mass m moving with speed v compresses a spring through a distance x before its speed is halved. What is the value of spring constant?

Tejveer is the medical student in Meerut. His grandfather went to Meerut to visit his grandson. In the evening his grandfather asked him about the heartbeats and pulse. He also eager to know what is the difference between the heartbeats of mammals relative to monkey. Tejveer being a medical student explained all about it very well.
(i) What values of Tejveer displayed here?
(ii) What is the scale factor of human relative to monkey?
(iii) What is the monkey's heart rate?