Class Notes NCERT Solutions for CBSE Students
Question: Certain force acting on a 20 kg mass changes its velocity from 5 ms-1 to 2 ms-1. Calculate the work done by the force.
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Question:. A certain household has consumed 250 units of energy during a month. How much energy is this in joule?
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Question: An electric heater is rated 1500 W. How much energy does it use in 10 hours?
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Question: Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 kmh-1?
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Question: Find the energy in kWh consumed in 10 hours by four devices of power 500 W each.
Answer:
Total power of 4 devices = 4 × 500 = 2000 W = 2 kW
Time = 10 h
Therefore, Energy consumed = Power × Time = 2 kW × 10 h = 20 kWh
Question: Two bodies of equal masses move with the uniform velocities v and 3v respectively. Find the , ratio of their kinetic energies.
Answer:
Thus, the kinetic energy of the second body is nine times the kinetic energy of the first body.
Question: A man of mass 60 kg runs up a flight of 30 steps in 40 seconds. If each step is 20 cm high, calculate the power of the man.
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Question: Calculate the amount of work done in moving a 50 kg block through a distance of 10 m by applying a force of 100 N.
Answer: Work done in moving a body through a certain distance is given by the expression, W = FScosθ = FS, here m = 50 kg, S = 10 m. Therefore, W = FS = 100 × 50 = 5000 J.
