9th Class Science Work and energy Question Bank

done Work Power and Energy Formative Subjective Problems Total Questions - 39

• question_answer1)
  How much work is done by a force of \[{{10}^{6}}\] dynes in moving an object moving through a distance of 1 m in the direction of force?
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• question_answer2)
  A body at rest has mass 10 kg. It is moved by a horizontal force of 5N on a horizontal surface. Calculate the work done by the force in 8s.
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• question_answer3)
  If a servant lifts \[10\,{{m}^{3}}\] of liquid from a tank, which is at a depth of 40m. If the work done by him is 1600 J, then find the density of the liquid (take \[\text{g}=\text{1}0\text{m}{{\text{s}}^{-\text{2}}}\])
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• question_answer4)
  A car weighing 1000 kg and traveling at 30 m/s stops at a distance of 50 m, retarding uniformly. What is the force exerted on it by the brakes? What is the work done by the brakes?
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• question_answer5)
  A child pulls a toy car through a distance of 1 Om on a smooth horizontal floor. The string held in the child's hand makes an angle of \[\text{6}0{}^\circ \] with the horizontal surface. If the force applied by the child be 5N, calculate the work done by the child in pulling the toy car.
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• question_answer6)
  Calculate the work done in lifting 20 litres of water through a vertical height of 6m (assume \[\text{g}=\text{1}0\text{m}/{{\text{s}}^{\text{2}}}\], density of water\[=\text{1 g}/\text{cc}\])
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• question_answer7)
  If 784 J of work was done in lifting 20kg mass, then calculate the height through which it was lifted. (Take \[\text{g}=\text{9}.\text{8 m}{{\text{s}}^{-\text{2}}}\])
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• question_answer8)
  Find the work done from the graph given below.
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• question_answer9)
  A body does 20J of work in 5s. What is its power?
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• question_answer10)
  If an engine lifts \[4000\,\,{{m}^{3}}\] of water from a depth of 500 m in 40 minutes, then calculate. (i) Work done by the motor and (ii) Power of the motor [\[\text{g}=\text{1}0\text{ m}/{{\text{s}}^{\text{2}}}\], density of water\[=\text{1}{{0}^{\text{3}}}\text{kg }{{\text{m}}^{-\text{3}}}\]]
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• question_answer11)
  What is the power of a pump which takes 10 seconds to lift 100kg of water to a water tank situated at a height of 20 m? (\[\text{g}=\text{1}0\text{m}/{{\text{s}}^{\text{2}}}\])
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• question_answer12)
  An engine is employed to fill a tank of size \[\text{2m}\times \text{2m}\times \text{2m}\] with water in 5 minutes, lifting water from a well of depth 30 m. Find the power of the engine.
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• question_answer13)
  A man carries a load of 50 kg through a height of 40m in 25s. If the power of the man is 1568 W, then find his mass.
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• question_answer14)
  What horse power engine is required to lift 18.24 quintals of coal per minute from a mine 50 m deep?
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• question_answer15)
  How many 2.5 kg bricks can a man carry up a stair 3.6 m high in one hour, if he works at the average rate of 9.8 watt?
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• question_answer16)
  A boat is moving through the water, at the rate of 10 m/s. Its engine have a power of 50 kilowatts. Find the force which must be overcomed in moving through water.
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• question_answer17)
  The heart does 2.5J of work in each heart beat. How many times per minutes does it beat, if its power is 4 watt?
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• question_answer18)
  An electric motor of power 200W is used to drive the stirrer in a water bath. If 60% of the energy supplied to the motor is spent in stirring the water, then calculate the work done on the water in one minute.
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• question_answer19)
  In a factory, an electric bulb of 400W is used for 3 hours and electric motor of 0.4 horse power is used for 6 hours energy day. Calculate the cost of using the bulb and motor for 30 days, if the cost of electrical energy is 2.50 rupee per unit.
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• question_answer20)
  Find the power from the graph given below.
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• question_answer21)
  Calculate the kinetic energy of a body of mass 2 kg moving with a velocity of 0.1 m/s.
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• question_answer22)
  When the mass and velocity of the body are doubled, what happens to its kinetic energy.
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• question_answer23)
  A body is moving in a starting line with certain velocity. Another body with double the mass and half the velocity of the first, is moving in the straight line. What is the ratio of kinetic energy of 2nd body with the first body?
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• question_answer24)
  If the velocity of a body is tripled, then find the % change in K.E
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• question_answer25)
  If the mass of a body is changed to 16 times, then what should be the change in velocity, such that its K.E remains same?
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• question_answer26)
  Two bodies of masses \[{{m}_{1}}\] and  \[{{m}_{2}}\] are moving with equal kinetic energies. What is the ratio of their momentum?
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• question_answer27)
  Two bodies of mass \[{{m}_{1}}\] and \[{{m}_{2}}\] are moving with equal momentum. What is the ratio of their kinetic energies.
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• question_answer28)
  When the momentum of a body is doubled, how does its kinetic energy change?
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• question_answer29)
  If the kinetic energy of a body is doubled, then how does its momentum change?
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• question_answer30)
  If the momentum of a body is numerically equal to its kinetic energy, then what is the velocity of the body?
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• question_answer31)
  If two bodies of masses 2m and m have their kinetic energies in the ratio 8 : 1, then ratio of their momentum is ____.
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• question_answer32)
  If two bodies of masses 2m and m have their momenta in the ratio 8 : 1, then the ratio of their kinetic energies is _____.
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• question_answer33)
  If the momentum of a body is increased by 50%, then what would be the percentage increase in its kinetic energy?
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• question_answer34)
  A bag of rice weighs 200 kg. To what height should it be raised, so that its potential energy may be 9800 Joules? (Take \[\text{g}=\text{9}.\text{8m}{{\text{s}}^{-\text{2}}}\])
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• question_answer35)
  Two bodies A and B of equal mass are kept at heights of h and 2h respectively. What will be the ratio of their potential energies?
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• question_answer36)
  A 20 kg ball is thrown upwards with a speed of 6 m/s. Find its potential energy when it reaches the highest point. Also, find the maximum height it reaches (\[\text{g}=\text{9}.\text{8 m}{{\text{s}}^{-\text{2}}}\])
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• question_answer37)
  A body of mass 10 kg is projected up with a velocity of 19.6 m/s. Find the potential energy at its highest point.
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• question_answer38)
  A body of mass 10 kg is released from a point, where it posses an energy of 1920.8J. Find the velocity with which it hits the ground.
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• question_answer39)
  Two bodies of same mass posses the same potential energy, when they are at a height of 'h' and '4h' on the surface of earth and an unknown planet respectively. What will be weight of a body on the unknown planet, if its weight of earth is 600 N.
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