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১) ক্ষারীয় মৃত্তিকা ধাতুগুলির যােজ্যতা - 1/2/3/4 ​

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State the energy changes in the following cases while in use (i) an electric iron. (ii) a ceiling fan. 2. Define power and energy. 3. State the energy changes in the following while in use (i) burning of a candle (ii) steam engine 4. Rajan exerts a force of 150 N in pulling a cart at a constant speed of 10 m/s, Calculate the power exerted. 5. Calculate the change in the kinetic energy of a moving body, if Its velocity is reduced to 1/3rd of the initial velocity. 6. A girl of mass 35 kg climbs up from the first floor of a building at a height 4m above the ground to the third floor at a height 12 m above the ground. What will be the increase in her gravitational potential energy? (Take, g = 10 ms -2 ) 7. A ball is placed on a compressed spring. When the spring is released, the ball is observed to fly away. (i) What form of energy does the compressed spring possess? (ii) Why does the ball fly away? 8. A body of mass 0.2 kg falls from a height of 10 m to a height of 6 m above the ground. Find the loss in potential energy taking place in the body. (Take, g = 10 ms -2 ) 9. A moving body weighing 400 N possesses 500 J of KE. Calculate the velocity with which the body is moving. (Take, g = 10 m/s -2 ) 10.A body of mass 5 kg is moving with a velocity of 10 ms -1 . What will be the ratio of its initial kinetic energy and final kinetic energy, if the mass of the body is doubled and its velocity is halved? 11. What is the SI unit of energy? How is the electron volt (eV) related to it? 12.Two bodies A and B of equal mass are kept at heights 20 m and 30 m, respectively. Calculate the ratio of their potential energies. 13.The work done by the heart is 1 joule per beat. Calculate the power of the heart, if it beats 72 times in one minute. 14.If the power of a motor is 40 kW, at what speed does it raise a load of 20000 N? 15.A machine raises a load of 750 N through a height of 16 m in 5 s. Calculate the power at which the machine works.