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Using a horizontal force of 200 N, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?
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According to the third law of motion, when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move.
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A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
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A battery lights a bulb. Describe the energy changes involved in the process.
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What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
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A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.
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An electric heater is rated 1500 W. How much energy does it use in 10 hours?
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Find the energy in joules consumed in 10 hours by four devices of power 500 W each.
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Is the following statement true or false :
A rocket can propel itself in a vacuum.
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What is the force which produces an acceleration of 1 m /s2 in a body of mass 1 kg ?
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A girl weighing 25 kg stands on the tloor. She exerts a downward force of 250 N on the floor. What force does the floor exert on her ?
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Fill in the following blanks with suitable words :
Forces in a Newton’s third law pair have equal _____________ but act in opposite _____________.
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Why does a gunman get a jerk on firing a bullet ?
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If action is always equal to reaction, explain why a cart pulled by a horse can be moved.
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Explain how a rocket works.
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Do action and reaction act on the same body or different bodies ? How are they related in magnitude and direction ? Are they simultaneous or not ?
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If a man jumps out from a boat, the boat moves backwards. Why ?
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