Q2 : An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. Work is done whenever the given two conditions are satisfied: (ii) There is a displacement of the body caused by the applied force along the direction of the applied force. S= 8 m NCERT DC Pandey Sunil Batra HC Verma Pradeep Errorless. MCQ Questions for Class 9 Science with Answers were prepared based on the latest exam pattern. (i) A force acts on the body. When a force F displaces a body through a distance S in the direction of the applied force, then the work done Won the body is given by the expression: The work done is said to be negative … Question 8. 1 unit of energy is equal to 1 kilowatt hour (kWh). Answer: K.E. What will be change in its kinetic energy? If the direction of force is perpendicular to displacement, then the work done is zero. Kinetic energy is the energy possessed by a body by the virtue of its motion. Q14 : An electric heater is rated 1500 W. How much energy does it use in 10 hours? Where, = Kinetic energy of the object moving with a velocity, v 6)A moving bus,car,falling stone possesses kinetic energy. NCERT Solutions for Class 9 Science Chapter 11 PDF: Work and Energy chapter deals with concepts of conservation of energy, its types, and how work & energy are interrelated. Download free PDF of best NCERT Solutions , Class 9, Physics, CBSE- Work and Energy . 1 kWh = 3.6 x 106 J m= Mass of the object 1 unit of energy is equal to 1 kilowatt hour (kWh). Hence, in the absence of force, work done by the person on the bundle is zero. Q1 : Look at the activities listed below. The velocity of a body moving in a straight line is inereásed by applying constant force F, for some distance in the direction of motion. If a body of mass m is moving with a velocity v, then its kinetic energy is given by the expression, Q4 : Write an expression for the work done when a force is acting on an object in the direction of its displacement. What is the kinetic energy of an object? Hence, Soni is right. As the object touches the ground, all its potential energy gets converted into kinetic energy. Yes. Download free PDF of best NCERT Solutions , Class 9, Physics, CBSE- Work and Energy . Question 2: Write an expression for the kinetic energy of an object. Answer : The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. W= F x d = 56 Nm W= F x s. Q5 : Define 1 J of work. What is the work done in this case? v= Velocity of the object = 5 m s -1 Therefore we can say that kinetic energy is: Derivation of Kinetic Energy using Calculus. So the kinetic energy at rest should be zero. It comes to rest because air resistance resists its motion. The work done is said to be negative when … Q3. A body of mass 3.0kg and a body B of mass 10 kg are dropped simultaneously from a height of 9m. Q19 : Soni says that the acceleration in an object could be zero even when several forces are acting on it. Q12 : Can there be displacement of an object in the absence of any force acting on it? Average power is obtained by dividing the total amount of work done in the total time taken to do this work. The law of conservation of energy states that energy can be neither created nor destroyed. For example, a fast moving pebble can injure a person or break glass pane of window, energy of moving vehicle, a fast moving wind can damage many house, or wind can move blades of wind mill, etc. 7)A falling coconut, running athlete possesses kinetic energy. MCQ Questions for Class 9 Science with Answers were prepared based on the latest exam pattern. Answer: Expression for kinetic energyis m = Mass of the object v = Velocityof the object = 5 m s−1 Given that kinetic energy, = 25 J (i) If the velocityof an object is doubled, then v = 5 × 2 = 10 m s−1. Therefore, work done, W= 7 ÃƒÆ’Ã¢â‚¬”8 answered Jul 8 by KomalKumari (48.9k points) selected Jul 8 by Amrita01 . 1 kWh = 3.6 x 106 J (d) In this case, there is no displacement of the leaves of the plant. Question From class 9 Chapter WORK AND ENERGY Write an expression for kinetic energy of an object. Calculate the work done by the force. Is it a violation of the law of conservation of energy? Now we already know that kinetic energy is the energy that it possessed due to its motion. Expression for K.E - KINETIC ENERGY-K.E = 1/2 mv2. Write an expression for the kinetic energy of an object. Timefor which the heater has operated, T= 10 h During the transformation, the total energy remains conserved. Hence, the work done by gravity on the body is zero. The process does not violate the law of conservation of energy. Work done by the bullocks is given by the expression: Where, For example, a fast moving pebble can injure a person or break glass pane of window, energy of moving vehicle, a fast moving wind can damage many house, or wind can move blades of wind mill, etc. Justify your answer. Answer : In this case, the direction of force acting on the block is perpendicular to the displacement. Answer : (i) A force acts on the body. Kinetic energy is given by the expression, Where, = Kinetic energy of the object moving with a velocity, v. m= Mass of the object (i) Kinetic energy when the object was moving with a velocity 5 m s −1. Required fields are marked *. Kinetic energy when the object was moving with a velocity 2 m s −1. Answer : The derivation of kinetic energy using calculus is given below. Derivation : We know that, W = f x s but f = ma. is the kinetic energy. Explain your answer. Write an expression for kinetic energy of an object. are solved by group of students and teacher of Class 9, which is also the largest student community of Class 9. = ½ mv 2. 1 J is the amount of work done by a force of 1 N on an object that displaces it through a distance of 1 m in the direction of the applied force. Accordingly, the kinetic energy increases. Q 8. "Energy posses by a body by virtue of its motion is referred to as 'Kinetic Energy'". Kinetic Energy: The kinetic energy of an object moving with a certain velocity is the work done on the object to acquire that velocity. Books. Hence, the energy consumed by four equal rating devices in 10 h will be 4 x 5 kWh = 20 kWh = 20 Units. Answer : The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. Kinetic Energy Formula (Rotational) The rotational kinetic energy equation goes like this: K = (1/2) Iw 2 (It is the Rotational kinetic energy of an object with Moment of inertia I and angular velocity w) Types of Kinetic Energy. 2. Learn the Kinetic energy formula here. W=K 2-K 1 =ΔK-----(ii) Where, ΔK = change in KE of the object. Work done = Force ÃƒÆ’Ã¢â‚¬”Displacement (a) Energy possessed by a body due to its motion is called its kinetic energy.Kinetic energy is directly proportional to the mass and square of the velocity of the moving body. Therefore, work done by gravity is given by the expression, the kinetic energy formula derivation can be done using algebra and calculus. Kinetic energy is given by the expression, 3. (ii) There is a displacement of the body caused by the applied force along the direction of the applied force. The derivation of kinetic energy is given below so that students can understand the concept more effectively. Substituting in eq n 1, we get, W = 1/2 mv 2. So, when the velocity doubles, consequently the kinetic energy quadruples. Your email address will not be published. • A green plant is carrying out photosynthesis. • A sailboat is moving due to wind energy. But, there is a displacement along the motion of the object. Answer : A body of mass 25 g has a momentum of 0.40 kgm/s.Find its kinetic energy. Q 2 Page 152 - Write an expression for the kinetic energy of an object View Answer Q 3 Page 152 - The kinetic energy of an object of mass, m moving with a velocity of 5 m s–1 is 25 J. The kinetic energy of a body is the energy that it possessed due to its motion. Although, force of gravity is acting on the bundle, the person is not applying any force on it. Kinetic energy is a property of a moving object or particle and depends not only on its motion but also on its mass. work done by force = (Ek)2 – (Ek)5 Therefore, there is a displacement in the boat in the direction of force. Question 1. The law of conservation of energy is not violated because the energy lost by the pendulum to overcome friction is gained by its surroundings. Where, Q18 : In each of the following a force, Fis acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Where, Answer : Q11 : Define 1 watt of power: The kind of motion may be translation, rotation about an axis, vibration, or any combination of motions. Applied force, F = 140 N Hence, work is done by wind on the boat. For a uniformly moving object K 1 =mv 1 2 /2. Answer : Acceleration in an object could be zero even when several forces are acting on it. The energy possessed by a body by virtue of its motion is called kinetic energy. • An engine is pulling a train. But, displacement of the load is in the forward direction. Hence, the transformation of energy in the given situation can be shown as: Q4 : Certain force acting on a 20 kg mass changes its velocity from 5 m s -1to 2 m s -1. W = mas ….. (1) By 3 rd eq n of motion, v 2 = u 2 + 2as. Let us take it that the force acts on the object through the displacement. = where m = mass of the object and v = uniform velocity of the object. Answer: KE = \(\frac{1}{2}\) mv 2. ... Write an expression for the kinetic energy of an object Answer Kinetic energy of an object = ½ mv 2 Where m = Mass of object v = Velocity of object Subscribe to our Youtube Channel - https://you.tube/teachoo. (b) While carrying a load, the donkey has to apply a force in the upward direction. We have Provided Work and Energy Class 9 Science MCQs Questions with Answers to help students understand the concept very well. Kinetic energy is the energy an object possesses because of its motion. (e) An engine applies force to pull the train. So we can say that the kinetic energy is: Stay tuned with BYJU’S and learn various other derivation of Physics formulas. NCERT Exemplar Problems Class 9 Science – Work and Energy Multiple Choice Questions (MCQs) Question 1: When a body falls freely towards the earth, then its total energy (a) increases (b) decreases (c) remains constant (d) first increases and then decreases Answer: (c) Since, total energy of the system is always conserved, so when a […] Kinetic energy, form of energy that an object or a particle has by reason of its motion. Question 2 Page 152 - Chapter 11 Class 9 - Work and Energy. Work and Energy Class 9 MCQs Questions with Answers. Solution: Kinetic energy of an object, K.E. h= Vertical displacement = 0 Question 8. (b) Define kinetic energy. We have Provided Work and Energy Class 9 Science MCQs Questions with Answers to help students understand the concept very well. A body can do different amount of work in different time intervals. W= F ÃƒÆ’Ã¢â‚¬” S This is the formula of Kinetic energy of an object of mass m moving with speed v along a line. This discussion on Write an expression for the kinetic energy of an object.? NCERT Textbook for Class 9 Science – Page 152 Q1. Starting with the work-energy theorem and Newton’s second law of motion we can say that. Work and Energy CBSE Class 9 Science Chapter 11 - Complete explanation and Notes of the chapter ‘Work and Energy’.. Work, Power And Energy Class 9 Extra Questions Short Answer Type 2. Therefore, energy consumed = Power x Time Therefore, 250 units of energy = 250 x 3.6 x 106 = 9 x 108 J, Q10 : A certain household has consumed 250 units of energy during a month. Does this violate the law of conservation of energy? Copyright © 2015 - 2020 Toppers Bulletin. What will be its kinetic energy when its velocity is doubled? Hence, the energy consumed by the heater in 10 h is 15 kWh. Work done = Energy consumed by the heater If the velocity of the body is zero, then the kinetic energy will also be zero. When a force Facts on an object to displace it through a distance Sin its direction, then the work done Won the body by the force is given by: This theorem states that the net work on a system goes into kinetic energy. Power is given by the expression, Q3. Answer : This is the formula of Kinetic energy of an object of mass m moving with speed v along a line. What will be its kinetic energy when its velocity is doubled? m= Mass of the object The kinetic energy of an object of mass, m moving with a velocity of 5 m s–1 is 25 J. When a satellite moves around the Earth, then the direction of force of gravity on the satellite is perpendicular to its displacement. Answer : The field being ploughed is 15 m long. Energy consumed by an electric device can be obtained with the help of the expression for power, Therefore, the law of conservation of energy is not violated. K E = 1/2mv 2. • Food grains are getting dried in the sun. Discuss this question with your friends and teacher. It may be shown by calculation as follows: Suppose a body of mass m falls from point A, which is at height H from the surface of earth. The derivation of kinetic energy is one of the most common questions asked in the examination. Question 2 Page 152 - Chapter 11 Class 9 - Work and Energy. K = 1 2 m u 2. Think. Answer : You can also get free sample papers, Notes, Important Questions. v 2 = 2as. Derive an expression for the kinetic energy of an object of mass m moving with a velocity V. (CBSE 2011, 2017) Answer: (a) Definition of energy : The capacity of doing work by a body or an object is known as the energy of the body or the object. This discussion on Write an expression for the kinetic energy of an object.? Kinetic energy - The energy possessed by virtue of its motion is said to be kinetic energy. Where is the energy you spend going? When we push a huge rock, there is no transfer of muscular energy to the stationary rock. Work done by force is equal to the change in kinetic energy. Answer : Power rating of the device, P= 500 W = 0.50 kW The corresponding relativistic expression for kinetic energy can be obtained from the work-energy theorem. (i) A force acts on the body. Q8 : Write an expression for the kinetic energy of an object. Work done by force is equal to the change in kinetic energy. (ii) If velocity is increased three times, then its kinetic energy becomes 9 times its original value, because it is proportional to the square of the velocity. This is because when the body falls from a height, then its potential energy changes into kinetic energy progressively. Q3 : When do we say that work is done? Since, displacement is perpendicular to force, the work done is zero. Work, Power And Energy Class 9 Extra Questions Short Answer Questions-II. To mass and speed by the application of force = m.v 2 2 /2, is the final points the! 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