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Important Questions on Linear Inequalities

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The number of natural numbers less than 7000 which can be formed by using the digits 0, 1, 3, 7, 9 (repetition of digits allowed) is equal to:
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For a particle performing linear SHM, its average speed over one oscillation is (A= amplitude of S.H.M., n= frequency of oscillation)
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A particle of mass m is moving in a circular path of constant radius r such that its centripetal acceleration ac is varying with time t as ac=k2rt2 , where k is a constant. The power delivered to the particle by the force acting on it is -
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Determine the power of an engine required to lift 100000 kg of coal per hour from a mine which is 360 m deep. (g = 10 m/s2)

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The engine of a train has to apply a force of 5000 N to overcome friction to run at a uniform rate of 90 km/h. What is the power developed by the engine?
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A box is moved along a straight line by a machine delivering constant power. The distance moved by the body in time t is proportional to
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A family uses 8 kW of power. 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? Compare this area to that of the roof of a typical house.
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An old man does 200 J of work in 10 s and a young man does 100 J of work in 4 s. (i) Who is delivering more power? (ii) Find the ratio of the power delivered by the old man to that delivered by the young man.
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A force F = 2 i ^ + 2 j ^ N displaces a particle through S = 2 i ^ + 2 k ^ m in 16 s. The power developed by F  is
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An engine accelerates a car of mass 800 kg to a speed of 72 km h-1 in 32 seconds. If the frictional force is 10 N per ton, the power developed by the engine is
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A machine gun fires six bullets per second into a target. The mass of each bullet is 3 g and the speed 500 m s-1. The power delivered to the bullets is
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A boy of mass 40 kg climbs up stairs of 50 steps, each of 10 cm high, in 5 s. Find the power developed by the boy. (g = 10 m/s2)
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An electric pump is used to fill an overhead tank of capacity 9m3 kept at a height of 10 m above the ground .If the pump takes 5 min to fill the tank by consuming 10 KW .power the efficiency of the pump should be (Take g=10 ms-2)
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An object does 20 J of work in 5 seconds. What is its power?
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A car of mass (m) accelerates, starting from rest, while the engine supplies constant power P. Then velocity varies with time (t) as

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A body is moving uni-directionally under the influence of a source of constant power. Its displacement in time t is proportional to
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The work done by the heart is 1 J per beat. Find the power of the heart if it beats 72 times per minute.
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Two girls A and B each of weight 400 N, climb up a tree of a height of 8 m. Girl A takes 20 s while B takes 50 s to accomplish this task. What is the power expended by each girl?
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A car of mass 1000 kg moves at a constant speed of 20 m s-1 up an incline. Assume that the frictional force is 200 N and that where, θ is the angle of the incline to the horizontal. sinθ=120, g=10 m s-2. Find the power developed by the engine