Page 1 : CHAPTER- 11, WORK, ENERGY & POWER, List two conditions which need to be satisfied for the work to be done on an object., A coolie is walking on a railway platform with a load of 27 kg on his head. What is the amount of work done by him?, Name the two common forms of mechanical energy., When an arrow is shot from its bow, it has kinetic energy. From where does it get this kinetic energy?, Explain the following terms with one example each: (a) Positive work (b) Zero work, Give any two uses of kinetic energy., What is the relationship between the commercial unit and SI unit of energy?, Calculate the work done against the gravity., What types of energy transformation takes place in the following:, (i) Electric heater, (ii) Solar battery, (iii) Dynamo, (iv) Steam engine and, (v) Hydroelectric power station?, A boy is pulling a cart by supplying a constant force of 8N on a straight path of 20m. On a roundabout of 10m diameter he forgets the path and take 1.5 turns and then continues on the straight path for another 20 m. Find the net work done by the boy on the cart., A man of mass 60 kg runs up a flight of 30 steps in 15 seconds. If each step is 20 cm high, calculate the power developed by the man. (Take g = 10 m/)., Find the velocity of a body of mass 100 g having a kinetic energy of 20 J., The speed of a vehicle of mass 500 kg increases from 36 km/h to 72 km/h. Calculate the increase in its kinetic energy., A machine raises a load of 750 N through a height of 16 m in 5 seconds. Calculate the power at which the machine works., If the power of a motor is 40 kW, at what speed can it raise a load of 20,000 N?, An engine can pump 30,000 litres of water to a vertical height of 45 metres in 10 minutes. Calculate the work done by the machine and its power. [g = 9.8 m/s2; Density of water = 103 kg/m3, 1000 litre = 1 m3]., Calculate the electricity bill for a month of 30 days, if the following devices are used as specified:, (a) 2 bulbs of 40W for 6 hours., (b) 2 tubelights of 50W for8 hours, (c) A TV of 120W for 6 hours, Given the cost of electricity is ₹2.50 per unit., (a) Two masses in the ratio 1 : 4 have their speeds in the ratio 4 : 5. Find the ratio of, their kinetic energy., (b) The heart does 1.5 J of work in every beat. How many times per minute does it beat, if its power is 2W?, A car of mass 900 kg is travelling at a steady speed of 30 m/s against a resistive force of 2000 N, as illustrated in figure., (i) Calculate the kinetic energy of the car., (ii) Calculate the energy used in 1.0 s against the resistive force., (iii) What is the minimum power that the car engine has to deliver to the wheels?, (iv) What form of energy is in the fuel used by the engine to drive the car?, Two workmen are employed on a building project, as shown in figure., (i) Workman 1 drops a hammer, which falls to the ground. The hammer has a mass of, 2.0 kg, and is dropped from a height of 4.8 m above the ground., (a) Calculate the change in gravitational potential energy of the hammer when it is, dropped., (b) Describe the energy changes from the time the hammer leaves the hand of workman, 1 until it is at rest on the ground., (ii) Workman 2 picks up the hammer and takes it back, up the ladder to workman 1. He, climbs the first 3.0 m in 5.0 s. His total weight, including the hammer, is 520 N., Calculate the useful power which his legs are producing.