(b) An object of mass 70 kg is raised to a height of 10 metres above the ground. Since work done is stored in kinetic energy. (g)Wind energy applies a force on the sailboat to push it in the forward direction. It comes to rest because air resistance resists its motion. m= Mass of the object Answer : Work done by gravity is given by the expression, 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. Answer : Answer : Both the methods are explained below. 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. Expression for kinetic energy is Q72: Define kinetic energy. Question 8. Through these solutions, we bring you the best in industry solutions for NCERT chapter 11 Class 9 science textbook question. Consider the case of an oscillating pendulum. The kinetic energy becomes zero, and the bob possesses only potential energy. Therefore, energy consumed = Power x Time Work done = Energy consumed by the lamp = 1000 J of body will also be zero.Kinetic energy is a scalar quantity like other forms of energies. ∴W= mg x 0 = 0 Where, K E = 1/2mv 2. Learn the Kinetic energy formula here. Kinetic energy depends upon the mass and velocity of body. Q3. Case III. Therefore, its kinetic energy becomes 4 times its original value, because it is proportional to the square of the velocity. The kind of motion may be translation, rotation about an axis, vibration, or any combination of motions. 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: Where is the energy you spend going? Question 2 Page 152 - Chapter 11 Class 9 - Work and Energy. Write an expression for the kinetic energy of an object. (b) Define kinetic energy. 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, Suppose an object is moving with constant velocity. You can also get free sample papers, Notes, Important Questions. (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. Q3. = 0.50 x 10 = 5 kWh Think. Write an expression for kinetic energy of an object. Average power is obtained by dividing the total amount of work done in the total time taken to do this work. as = 1/2 v 2. Hence, work is done by wind on the boat. 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. The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. Kinetic energy is a property of a moving object or particle and depends not only on its motion but also on its mass. 13.4k LIKES. Hence, work is done by Seema while swimming. Derivation : We know that, W = f x s but f = ma. Where K.E. Answer : (ii) Kinetic energy when the object was moving with a velocity 2 m s-1 Q15 : Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. To derive an expression for kinetic energy using calculus, we will not need to assume anything about the acceleration. What is the kinetic energy of an object? Hence, work is done by the wind mill in lifting water from the well. Therefore, its kinetic energy becomes 4 times its original value, because it is proportional to the square of the velocity. = where m = mass of the object and v = uniform velocity of the object. A decrease in the potential energy is equal to an increase in the kinetic energy of the body. What will be its kinetic energy when its velocity is doubled? v is the velocity with which body is moving. Given that kinetic energy, = 25 J Answer: K.E. 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 provides a velocity to the bicycle. The derivation of kinetic energy using calculus is given below. 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. Write an expression for the kinetic energy of an object. A body of mass 25 g has a momentum of 0.40 kgm/s.Find its kinetic energy. What will be change in its kinetic energy? derive equation for loss of kinetic energy in case of a completely inelastic collision in one dimension - Physics - TopperLearning.com | 98uzboee An important topic of NCERT Solutions for Class 9 Science Chapter 11 is : Energy: Energy is the capability of doing work. Hence, 2100 J of work is done in ploughing the length of the field. Hence, 20.8 x 104 J of work is required to stop the car. • An engine is pulling a train. W= mgh The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. Work is done whenever the given two conditions are satisfied: Acceleration in an object could be zero even when several forces are acting on it. Kinetic energy when the object was moving with a velocity 2 m s −1. The mechanical energy (kinetic energy + potential energy) of a freely falling object remains constant. Q3 : When do we say that work is done? 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. Objects in motion possess energy, we call this energy kinetic energy. Therefore, the work done by gravity on the given object is zero joule. 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. 6)A moving bus,car,falling stone possesses kinetic energy. Q3. (ii) There is a displacement of the body by the application of force in or opposite to the direction of force. is the kinetic energy. Obtain an expression for the kinetic energy of an object. Write an expression for the kinetic energy of an object. The work done is said to be negative … Answer : Hence, the work done is zero during the process of food grains getting dried in the Sun. Answer : How much work is done in ploughing the length of the field? The derivation of kinetic energy is given below so that students can understand the concept more effectively. Heat energy heats the rider’s body. Answer: (f) Food grains do not move in the presence of solar energy. Thus equation (i) becomes. Write an expression for the kinetic energy of an object. Displacement, d = 15 m 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: Yes. Every moving object possesses kinetic energy. the kinetic energy formula derivation can be done using algebra and calculus. Work done = Force x Displacement = 56 J. Q2 : When do we say that work is done? 7)A falling coconut, running athlete possesses kinetic energy. The law of conservation of energy is not violated because the energy lost by the pendulum to overcome friction is gained by its surroundings. Answer : (b) Define kinetic energy. Write an expression for the kinetic energy of an object. When the bulb receives this electrical energy, then it converts it into light and heat energy. 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? It is further classified into gravitational potential energy (GPE) and elastic potential energy … It can only be converted from one form to another. Question 1. Answer : Q73: (a) Derive an expression to calculate the kinetic energy of a body. Solution: Kinetic energy of an object, K.E. This discussion on Write an expression for the kinetic energy of an object.? When we push a huge rock, there is no transfer of muscular energy to the stationary rock. Download free PDF of best NCERT Solutions , Class 9, Physics, CBSE- Work and Energy . (b) While carrying a load, the donkey has to apply a force in the upward direction. Is it a violation of the law of conservation of energy? The energy possessed by a body by virtue of its motion is called 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. K = 1 2 m u 2. Whileriding a bicycle, the muscular energy of the rider gets transferred into heat energy and kinetic energy of the bicycle. Work and Energy Kinetic Energy . Substituting in eq n 1, we get, W = 1/2 mv 2. Copyright © 2015 - 2020 Toppers Bulletin. Velocity of car, v= 60 km/h Explain your answer. Mass = m . • A green plant is carrying out photosynthesis. This discussion on Mathematical expression of kinetic and potential energy is done on EduRev Study Group by Class 9 Students. Work done by the force of gravity on an object depends only on vertical displacement. =40-250 = -210 J Q 8. (i) A force acts on the body. Is the initial Kinetic of the object. Kinetic energy is the energy an object possesses because of its motion. v= Velocity of the object = 5 m s -1 Since, displacement is perpendicular to force, the work done is zero. Q6 : The potential energy of a freely falling object decreases progressively. What is its potential energy? at rest, u=0. 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