Numerical problems | Physics 9th | Chapter 6 | Work & Energy | KPK Textbook Board, Peshawar | SLO скачать в хорошем качестве

Numerical problems | Physics 9th | Chapter 6 | Work & Energy | KPK Textbook Board, Peshawar | SLO

Q. Choose the best possible option. Work done will be zero when the angle between force and displacement is (a) 30o (b) 45o (c) 60o (d) 90o 30N force is exerted and the trolley moves a distance of 5m in the direction of the force, the work done is (a) 6J (b) 25J (c) 150J (d) 0.17N If the speed of a car decreases by half, the kinetic energy change by factor (a) 4 (b) 2 (c) 1/2 (d) 1/4 An object of mass 10kg is lifted vertically through a height of 5m. The gravitational potential energy gained by the object is (a) 0.5J (b) 2J (c) 50J (d) 490J If a petrol engine does 20J of useful work for every 100J of energy supplied to it, then its efficiency is (a) 80% (b) 60% (c) 40% (d) 20% kWh is unit for (a) Energy (b) Power (c) Efficiency (d) None 1hp= (a) 476W (b) 550W (c) 746W (d) 1 ft.lb/s Hira weighing 500N takes 90s to reach the topo of a hill 18m high. Her average muscle power is (a) 2500W (b) 100W (c) 32.8W (d) 3.24W A machine is able to lift 200N of concrete slab vertically up to a height of 30m above the ground in 50s. The average power of the machine is (a) 1.33W (b) 60W (c) 120W (d) 6000W Q. Give a short response to the following questions Can a centripetal force ever do work on an object? Explain. What happens to the kinetic energy of a bullet when it penetrates into a sand bag? A meteor enters into earth’s atmosphere and burns. What happens to its kinetic energy? Two bullets are fired at the same time with the same kinetic energy. If one bullet has twice the mass of the other, which has the greater speed and by what factor? Which can do the most work? Can an object have different amounts of gravitational potential energy if it remains at the same elevation? Why do roads leading to the top of a mountain wind back and forth? Which would have a greater effect on the kinetic energy of an object, doubling the mass or doubling the velocity? If the speed of a particle triples, by what factor does its kinetic energy increase? The motor of a crane uses power P to lift a steel beam. By what factor must the motor’s power increase to lift the beam twice as high in half the time? Q. Solve the following numerical questions. Determine the work done in each of the following cases: a) Kicking soccer ball forward with a force of 40N over a distance of 15cm b) Lifting a 50kg barbell straight up 1.95m Calculate the velocity of a 1.2kg falling star (meteorite) with 5.5×〖10〗^8 J of energy. Calculate the gravitational potential energy of a 2000kg piano a) resting on the floor b) with respect to the basement floor, 1.9m below. An elevator weighing 5000N is raised to a height of 15.0m in 10.0s, how much power is developed? What power is required for a ski-hill chair lift that transports 500 people (average mass 65kg) per hour to an increased elevation of 1200m? How long will it take a 2750W motor to lift a 385kg sofa set to a sixth-story window 16.0m above? How much work can a 2.0hp motor do in 1.0h?