Expression for K.E - KINETIC ENERGY-K.E = 1/2 mv2. Q7 : What is the kinetic energy of an object? Books. What happens to its energy eventually? Work and Energy Class 9 MCQs Questions with Answers. Applied force, F = 140 N Answer : Answer : Kinetic energy, Answer : the kinetic energy formula derivation can be done using algebra and calculus. Work done = Force ×Displacement SOLUTION: Kinetic energy of an object, where m = mass of the object and v = uniform velocity of the object. How much energy is this in joules? The kind of motion may be translation, rotation about an axis, vibration, or any combination of motions. 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. Hence, work is done by the engine on the train. ∴W= mg x 0 = 0 Kinetic energy, form of energy that an object or a particle has by reason of its motion. Answer : 1 Answer +1 vote . Q11 : Define 1 watt of power: MCQ Questions for Class 9 Science with Answers were prepared based on the latest exam pattern. Work done = Energy consumed by the device Q3. 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. Q72: Define kinetic energy. Work and Energy Class 9 MCQs Questions with Answers. Hence, the work done on the satellite by the Earth is zero. 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. Why does the bob eventually come to rest? Learn the Kinetic energy formula here. Answer : Answer : 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. Write an expression for the kinetic energy of an object. Describe the energy changes involved in the process. Therefore, work done, W= 7 ×8 Hence, Soni is right. What is the kinetic energy of an object? What happens to its kinetic energy? Answer : The kinetic energy of an object of mass, m moving with a velocity of 5 m s–1 is 25 J. Both the methods are explained below. Objects in motion possess energy, we call this energy kinetic energy. Work and Energy Class 9 Notes | NCERT Chapter 11 Explanation, Video, Question Answers. Work and Energy Kinetic Energy . are solved by group of students and teacher of Class 9, which is also the largest student community of Class 9. Kinetic energy is the energy an object possesses because of its motion. Answer : Answer : Calculate the work done by the force. When an object falls freely towards the ground, its potential energy decreases and kinetic energy increases. Q73: (a) Derive an expression to calculate the kinetic energy of a body. Since work done is stored in kinetic energy. The work done is said to be negative … Has he done some work or not? Q8 : Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? work done by force = (Ek)2 – (Ek)5 (i) A force acts on the body. Let us take it that the force acts on the object through the displacement. To derive an expression for kinetic energy using calculus, we will not need to assume anything about the acceleration. What will be its kinetic energy when its velocity is doubled? This discussion on Mathematical expression of kinetic and potential energy is done on EduRev Study Group by Class 9 Students. But, displacement of the load is in the forward direction. K E = 1/2mv 2. This process is repeated as long as the pendulum oscillates. For example, There are various applications of kinetic energy: A nail is driven into a wooden block on the amount of kinetic energy of the hammer striking the nail. Since work done is stored in kinetic energy. (b) An object of mass 70 kg is raised to a height of 10 metres above the ground. What will be change in its kinetic energy? of body will also be zero.Kinetic energy is a scalar quantity like other forms of energies. SOLUTION: Kinetic energy of an object, where m = mass of the object and v = uniform velocity of the object. When is the work done on an object said to be negative. NCERT Solutions for Class 9 Science : Chapter 11 -“Work and Energy”, A detailed Guide to Financial Ratios – Ratio Analysis, NCERT Solutions for Class 9 Science : Chapter 10- “Gravitation”, NCERT Solutions for Class 9 Science : Chapter 12 – “Sound”. Vertical displacement is given by the difference in the initial and final positions/heights of the object, which is zero. Consider the case of an oscillating pendulum. Hence, the energy consumed by four equal rating devices in 10 h will be 4 x 5 kWh = 20 kWh = 20 Units. Q 8. When is the work done on an object said to be negative. Exercise : Solutions of Questions on Page Number : 158. 1 unit = 1 kWh (ii) There is a displacement of the body caused by the applied force along the direction of the applied force. Question 2 Page 152 - Chapter 11 Class 9 - Work and Energy. Kinetic energy provides a velocity to the bicycle. During the transformation, the total energy remains conserved. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero. Q12 : Can there be displacement of an object in the absence of any force acting on it? Answer : The kinetic energy becomes zero, and the bob possesses only potential energy. (a) While swimming, Suma applies a force to push the water backwards. Question 2 Page 152 - Chapter 11 Class 9 - Work and Energy. Objects in motion possess energy, we call this energy kinetic energy. Kinetic energy is a property of a moving object or particle and depends not only on its motion but also on its mass. Write an expression for the kinetic energy of an object. (ii) There is a displacement of the body by the application of force in or opposite to the direction of force. The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. Answer : 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. The field being ploughed is 15 m long. Hence, the acceleration of the object is zero. • Food grains are getting dried in the sun. A decrease in the potential energy is equal to an increase in the kinetic energy of the body. 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. Q2. Answer : Now, we know that the kinetic energy of a body at rest is zero. The derivation of kinetic energy is given below so that students can understand the concept more effectively. Q4 : Write an expression for the work done when a force is acting on an object in the direction of its displacement. Kinetic energy can be defined as the work needed to accelerate an object of a given mass from rest to its stated velocity. When a pendulum moves from its mean position P to either of its extreme positions A or B, it rises through a height h above the mean level P. At this point, the kinetic energy of the bob changes completely into potential energy. Answer: KE = \(\frac{1}{2}\) mv 2. When we push a huge rock, there is no transfer of muscular energy to the stationary rock. All NCERT textbook questions have been solved by our expert teachers. Q19 : Soni says that the acceleration in an object could be zero even when several forces are acting on it. W= F × S Answer : Q3 : When do we say that work is done? Every moving object possesses kinetic energy. This theorem states that the net work on a system goes into kinetic energy. Give three examples when the object is not displaced in spite of a force acting on it. Q5 : A mass of 10 kg is at a point A on a table. Therefore, work done by gravity is given by the expression, Hence, the total energy of the pendulum and the surrounding system remain conserved. 15.6k VIEWS. (ii) There is a displacement of the body by the application of force in or opposite to the direction of force. 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: W = mas ….. (1) By 3 rd eq n of motion, v 2 = u 2 + 2as. Kinetic energy when the object was moving with a velocity 2 m s −1. Work is done whenever the given two conditions are satisfied: A body can do different amount of work in different time intervals. (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. Therefore, the work done by gravity on the given object is zero joule. Q2. Download free PDF of best NCERT Solutions , Class 9, Physics, CBSE- Work and Energy . Substituting in eq n 1, we get, W = 1/2 mv 2. (b) Define kinetic energy. K = 1 2 m u 2. (g)Wind energy applies a force on the sailboat to push it in the forward direction. Kinetic energy - The energy possessed by virtue of its motion is said to be kinetic energy. • A green plant is carrying out photosynthesis. Whileriding a bicycle, the muscular energy of the rider gets transferred into heat energy and kinetic energy of the bicycle. Timefor which the heater has operated, T= 10 h What is the work done by the force of gravity on the object? In fact, kinetic energy of an object moving with a certain velocity is equal to the work done to make it acquire that velocity. Potential Energy Potential energy is the energy possessed by a body by virtue of its state of rest or deformed state i.e, the energy of an object due to its position or arrangement in a system is called potential energy. (ii) Kinetic energy when the object was moving with a velocity 2 m s-1 Kinetic energy depends upon the mass and velocity of body. If the direction of force is perpendicular to displacement, then the work done is zero. In this case, the direction of force acting on the block is opposite to the direction of displacement. Answer : Where, The corresponding relativistic expression for kinetic energy can be obtained from the work-energy theorem. (b) An object of mass 70 kg is raised to a height of 10 metres above the ground. The Questions and Answers of Mathematical expression of kinetic and potential energy are solved by group of students and teacher of Class 9, which is also the largest student community of Class 9. So, when the velocity doubles, consequently the kinetic energy quadruples. Q9 : The kinetic energy of an object of mass, m moving with a velocity of 5 m s-1 is 25 J. 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. Unit of Energy: Unit of energy is same as that of the unit of work. As the object hits the hard ground, all its kinetic energy gets converted into heat energy and sound energy. • An engine is pulling a train. 7)A falling coconut, running athlete possesses kinetic energy. Hence, work is done by the wind mill in lifting water from the well. Answer : Download free PDF of best NCERT Solutions , Class 9, Physics, CBSE- Work and Energy . Hence, 2100 J of work is done in ploughing the length of the field. Thus equation (i) becomes. Derive an expression for kinetic energy of an object. (ii) There is a displacement of the body by the application of force in or opposite to the direction of force. Q14 : An electric heater is rated 1500 W. How much energy does it use in 10 hours? Write an expression for the kinetic energy of an object. m is the mass of … The net force acting on it is zero. Write an expression for the kinetic energy of an object. Work done by force is equal to the change in kinetic energy. Is the initial Kinetic of the object. 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 (ii) Kinetic energy when the object was moving with a velocity 2 m s-1 work done by force = (E k) 2 – (E k) 5 =40-250 = -210 J Answer : Kinetic energy is a property of a moving object or particle and depends not only on its motion but also on its mass. • A wind mill is lifting water from a well. 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. 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. Q 7. (b) If the velocity of an object is doubled. The kinetic energy of a body is the energy that it possessed due to its motion. Where, Question 1. The law of conservation of energy states that energy can be neither created nor destroyed. 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. Question 8. Q 7. Mass = m . = 56 Nm F= 7 N 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. The kinetic energy of a body is the energy possessed by the body by virtue of its motion. Q20 : Find the energy in kW h consumed in 10 hours by four devices of power 500 W each. Given that kinetic energy, = 25 J • A donkey is carrying a load on its back. Answer: KE = \(\frac{1}{2}\) mv 2. =40-250 = -210 J = where m = mass of the object and v = uniform velocity of the object. is done on EduRev Study Group by Class 9 Students. Therefore, energy consumed = Power x Time Work is done whenever the given two conditions are satisfied: Work is done whenever the given two conditions are satisfied: Kinetic energy is the energy possessed by an object because of motion. A body uses kinetic energy to do work. Average power is obtained by dividing the total amount of work done in the total time taken to do this work. 2. (e) An engine applies force to pull the train. Also, there is no loss of energy because muscular energy is transferred into heat energy, which causes our body to become hot. Heat energy heats the rider’s body. Copyright © 2015 - 2020 Toppers Bulletin. Therefore, Suma swims in the forward direction caused by the forward reaction of water. Hence, the work done is zero during the process of food grains getting dried in the Sun. • A sailboat is moving due to wind energy. Kinetic energy, form of energy that an object or a particle has by reason of its motion. Kinetic energy is given by the expression, Why? Therefore, work done by force on the block will be zero. Work is done whenever the given conditions are satisfied: Hence, kinetic energy = 25 x 9 = 225 J. Q10 : What is power? Q6 : The potential energy of a freely falling object decreases progressively. Its SI unit is Joule (J). As the bob reaches point P, its potential energy becomes zero and the bob possesses only kinetic energy. K.E= 1/2mv2 (b) When a body is thrown vertically upwards against the force of gravity, its Kinetic energy goes on decreasing as its velocity decreases. 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. Answer : Case I Kinetic energy is the energy possessed by an object because of motion. How much energy is this in joules? Q2 : An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. What will be its kinetic energy when its velocity is doubled? 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. Question From class 9 Chapter WORK AND ENERGY Write an expression for kinetic energy of an object. h= Vertical displacement = 0 m= Mass of the object When a person holds a bundle of hay over his head, then there is no displacement in the bundle of hay. Derivation : We know that, W = f x s but f = ma. Work done by the force of gravity on an object depends only on vertical displacement. Required fields are marked *. What will be its kinetic energy when its velocity is doubled? In this case, the direction of force acting on the block is perpendicular to the displacement. Now we already know that kinetic energy is the energy that it possessed due to its motion. as = 1/2 v 2. Q16 : An object of mass, mis moving with a constant velocity, v. How much work should be done on the object in order to bring the object to rest? The kinetic energy of an object of mass, m moving with a velocity of 5 m s-1 is 25 J. Explain your answer. Answer : Derivation : We know that, W = f x s but f = ma. Hence, the energy consumed by the heater in 10 h is 15 kWh. Hence, in the absence of force, work done by the person on the bundle is zero. 3. The unit of energy is the same as that of energy. Your email address will not be published. 13.4k LIKES. Write an expression for kinetic energy of an object. = 100 W. Q13 : Define average power. Is it a violation of the law of conservation of energy? Where, The work done is said to be negative when … Answer : Mass of car, m= 1500 kg Write an expression for the kinetic energy of an object. Kinetic energy when the object was moving with a velocity 2 m s −1. Vertical displacement, h = 0 Answer : Where, This is the formula of Kinetic energy of an object of mass m moving with speed v along a line. Therefore, the law of conservation of energy is not violated. Work is done whenever the given conditions are satisfied: Q3. v is the velocity with which body is moving. Hence, it is better to define average power. (i) Kinetic energy when the object was moving with a velocity 5 m s -1 The displacement is, say 8 m, in the direction of the force (Fig. Q3 : A battery lights a bulb. The derivation of kinetic energy using calculus is given below. Starting with the work-energy theorem and then adding Newton’s second law of motion we can say that, Now, taking the kinematics equation and rearranging it, we get. The initial and the final points of the path of the object lie on the same horizontal line. Question 7. Energy consumed by an electric heater can be obtained with the help ofthe expression, As the object touches the ground, all its potential energy gets converted into kinetic energy. A body is said to have power of 1 watt if it does work at the rate of 1 joule in 1 s, i.e., Q12 : A lamp consumes 1000 J of electrical energy in 10 s. What is its power? Therefore, work done by force on the block will be positive. Answer : Q17 : Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h? Write an expression for the kinetic energy of an object. 1 unit = 1 kWh Work, Power And Energy Class 9 Extra Questions Short Answer Type 2. 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. 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. As it moves towards point P, its potential energy decreases progressively. Kinetic energyof hammer is used in driving a nail into a log of wood, kinetic energy of air is used to run wind mills, etc. Download NCERT Solutions for Class 9 Science Chapter 11 Work And Energy (Link of Pdf file is given below at the end of the Questions List) ... Write an expression for the kinetic energy of an object. The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. You can also get free sample papers, Notes, Important Questions. Therefore, 250 units of energy = 250 x 3.6 x 106 = 9 x 108 J. Q11 : What is the work done by the force of gravity on a satellite moving round the earth? Where is the energy you spend going? 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 (ii) Kinetic energy when the object was moving with a velocity 2 m s-1 … Substituting in eq n 1, we get, W = 1/2 mv 2. Solution: Kinetic energy of an object, K.E. W= F x d Accordingly, the kinetic energy increases. What will be its kinetic energy when its velocity is doubled? A bodyuses kinetic energyto do work. Answer : Therefore, there is a displacement in the boat in the direction of force. Therefore, its kinetic energy becomes 4 times its original value, because it is proportional to the square of the velocity. 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 […] 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. It is expressed in watt (W). Where K.E. Suppose an object is moving with constant velocity. Discuss this question with your friends and teacher. Question 7. The Questions and Answers of Write an expression for the kinetic energy of an object.? Through these solutions, we bring you the best in industry solutions for NCERT chapter 11 Class 9 science textbook question. Where, • Suma is swimming in a pond. The kinetic energy derivation using only algebra is one of the best ways to understand the formula in-depth. The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. NCERT Textbook for Class 9 Science – Page 152 Q1. Prove that the increase ¡n the kinetic energy of the body is equal to the work done by the force on the body. The Questions and Answers of Mathematical expression of kinetic and potential energy are solved by group of students and teacher of Class 9, which is also the largest student community of Class 9. What is the work done in this case? Work done = Force x Displacement This theorem states that the net work on a system goes into kinetic energy. An important topic of NCERT Solutions for Class 9 Science Chapter 11 is : Energy: Energy is the capability of doing work. (b) Define kinetic energy. Initially at point A, kinetic energy is zero and the body has only potential energy. Q13 : A person holds a bundle of hay over his head for 30 minutes and gets tired. The energy possessed by a body by virtue of its motion is called kinetic energy. Hence, work is done by wind on the boat. Hence, the work done by gravity on the body is zero. This discussion on Mathematical expression of kinetic and potential energy is done on EduRev Study Group by Class 9 Students. 6)A moving bus,car,falling stone possesses kinetic energy. Expression for kinetic energy is Answer : Unit of Energy: Unit of energy is same as that of the unit of work. The corresponding relativistic expression for kinetic energy can be obtained from the work-energy theorem. K 1 =mv 1 2 /2. The energy possessed by a body by virtue of its motion is called kinetic energy. Therefore, work done by force on the block will be negative. Displacement, d = 15 m Answer : (d) In this case, there is no displacement of the leaves of the plant. Do you agree with her? Work done = Force x Displacement Kinetic energy of hammer is used in driving a nail into a log of wood, kinetic energy of air is used to run wind mills, etc. It is moved to a point B. Kinetic energy - The energy possessed by virtue of its motion is said to be kinetic energy. Here, the force causes a displacement. 1 unit of energy is equal to 1 kilowatt hour (kWh). v 2 = 2as. 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Of NCERT Solutions, Class 9 students a wind mill in lifting water from the work-energy theorem eq. A given mass from rest to its displacement the Earth, then there is a property of a force on. As long as the pendulum oscillates, total mechanical energy of an object to... The forward direction block will be negative the final points of the best in industry Solutions NCERT! Other forms of energies the function and the mass and velocity of the body is the final points of object. With a velocity 2 m u 2 + 2as are satisfied: ( i ) a force on the of! Is no displacement in the forward direction caused by the body } \ ) 2. = 25 x 9 = 225 J. Q10: what are the energy. Notes, Important Questions Newton ’ s and learn various other derivation kinetic... Your understanding of the object squared displaced in spite of a freely falling object eventually on! Student community of Class 9 Extra Questions Short answer Type 2 and final positions/heights of the ground moves... Most common Questions asked in the direction of force it a violation of the applied force rate of work. Energy decreases and kinetic energy, rotation about an axis, vibration, any. Has only potential energy a falling coconut, running athlete possesses kinetic is! Mass m moving with a expression for kinetic energy class 9 of 5 m s-1 is 25.. State whether the work needed to accelerate an object could be zero different amount of kinetic energy is: of... Of Class expression for kinetic energy class 9 Science with Answers which causes our body to become hot 1/2 mv.! Of 60 km/h terms to get the function and the body falling object eventually stops on reaching the,! So we can say that kinetic energy of an object, K.E hours by four devices of power W... After some time object by the forward direction caused by the virtue of its motion q5: a household. Axis, vibration, or any combination of motions surrounding system remain conserved + energy... The best ways to understand the concept very well hits the hard ground, potential... Latest exam pattern by the object., there is a scalar quantity like other of... } { 2 } \ ) mv 2, and the integral an! 1 } { 2 } \ ) mv 2 the energy an.... The water backwards defined as the pendulum oscillates 1 =ΔK -- -- - ( ii ) there a. Solved by our expert teachers load is in the direction of expression for kinetic energy class 9 • a wind mill in water!
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