Tiêu đề Class 09 Science Chapter 11 Work and Energy.pdf ✅

Work and Energy DPP-01 [Topic: Work] Very Short Answer Type Questions 1. When do we say that work is done? 2. Write an expression for the work done when a force is acting on an object in the direction of its displacement. 3. A pair of bullocks exerts a force of 140N on a plough. The field being ploughed is 15m long. How much work is done in ploughing that length of the field? 4. A student is writing a three hours science paper. How much work is done by the student? Give reason for your answer. 5. A coolie is walking on a railway platform with a load of 30kg on his head. How much work is done by the coolie? 6. Calculate the work done when a force of 15N moves a body by 5m in its direction. 7. A bag of cement has a mass of 20kg. A fork lift raised three bags of cement to 80cm from the ground on the truck. What is work done by fork lift? 8. Define 1J of work. Short Answer Type Questions-I 9. An object thrown at a certain angle with the ground traces in a curved path and falls back to the ground. The initial and final point of the path of the object lies on the same horizontal line. What is the work done by the force of gravity on the object? 10. List two essential conditions for work to be done. 11. Given below are a few situations, study them and state in which of given cases work is said to be done. Give reason for your answer. (a) A person is pushing hard a huge rock but the rock does not move. (b) A bullock is pulling a cart up to 1km on the road. (c) A girl is pulling a trolley for about 2m distance. (d) A student standing in the sun for two hours with a heavy bag on his head. 12. A force of 7N acts on an object. The displacement is, say 8m, in the direction of the force as shown in the figure. Let us take that a constant force acts on the object through the displacement. What is the work done in this case? Short Answer Type Questions-II 13. Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term 'work'.
(i) Suma is swimming in a pond. (ii) A donkey is carrying a load on its back. (iii) A wind-mill is lifting water from a well. (iv) A green plant is carrying out photosynthesis. (v) An engine is pulling a train. (vi) Food grains are getting dried in the sun. (vii) A sail boat is moving due to wind energy. 14 A porter lifts a luggage of 15kg from the ground and puts it on his head 1.5m above the ground. Calculate the work done by him on the luggage. (gg = 9.8ms−2)
Work and Energy DPP-02 [Topic: Energy] Very Short Answer Type Questions 1. What is Kinetic energy of an object? 2. Write an expression for the kinetic energy (K.E.) of the object. 3. What is Power? 4. Define 1 Watt power. 5. A lamp consumes 1000J of electrical energy in 10s. What is its power? 6. Define average power. 7. An electric bulb of 60W is used for 6 hours per day. Calculate the 'units' of energy consumed in one day by the bulb. 8. A battery lights a bulb. Describe the energy changes involved in the process. 9. What are the various energy transformations that occur when you are riding a bicycle? 10. A certain household has consumed 250 units of energy during a month. How much energy is this expressed in joules? 11. When a body falls freely towards the earth, then what happens to its total energy? 12. What type of energy is possessed by water stored in a dam? 13. A body is falling from a height ' h '. After it has fallen to a height, h 2 what type of energy will be possessed by the body? Short Answer Type Questions-I 14. An electric motor can lift a weight of 2000N through a vertical height of 10m in 20s. What is the power of this motor? 15. A cell will deliver 3000J of energy to a 2W electric motor before the cell gets exhausted. For what period of time will the motor run? 16. An object of mass 15kg is moving with a uniform velocity of 4ms−1. What is the kinetic energy possessed by the object? 17. Find the energy possessed by an object of mass 10kg when it is at a height of 6m above the ground. (Given, gg = 9.8ms−2 ). 18. An object of mass 12kg is at a certain height above the ground. If the potential energy of the object is 480J, find the height at which the object is with respect to the ground. Given, gg = 10ms−2.