Answer : What will be its kinetic energy when its velocity is doubled? Physics. 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. Where, 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. • An engine is pulling a train. Q1 : Look at the activities listed below. 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? A bodyuses kinetic energyto do work. (ii) There is a displacement of the body by the application of force in or opposite to the direction of force. Answer : Therefore, the work done is zero. The kinetic energy derivation using only algebra is one of the best ways to understand the formula in-depth. the kinetic energy formula derivation can be done using algebra and calculus. Q4 : Write an expression for the work done when a force is acting on an object in the direction of its displacement. of body will also be zero.Kinetic energy is a scalar quantity like other forms of energies. Question 1. Q21 : A freely falling object eventually stops on reaching the ground. as = 1/2 v 2. Sol. Question 1. (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. (a) While swimming, Suma applies a force to push the water backwards. Q9 : A certain household has consumed 250 units of energy during a month. The law of conservation of energy states that energy can be neither created nor destroyed. Answer : The derivation of kinetic energy using calculus is given below. The corresponding relativistic expression for kinetic energy can be obtained from the work-energy theorem. Therefore, there is a displacement in the boat in the direction of force. NCERT Textbook for Class 9 Science – Page 152 Q1. Derive an expression for kinetic energy of an object. Work, Power And Energy Class 9 Extra Questions Short Answer Questions-II. Answer : Derivation : We know that, W = f x s but f = ma. (b) Define kinetic energy. When a person holds a bundle of hay over his head, then there is no displacement in the bundle of hay. How much work is done in ploughing the length of the field? m= Mass of the object Yes. are solved by group of students and teacher of Class 9, which is also the largest student community of Class 9. The bob does not oscillate forever. 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. Hence, 2100 J of work is done in ploughing the length of the field. ... 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 - … It is expressed in watt (W). Work and Energy Class 9 Notes | NCERT Chapter 11 Explanation, Video, Question Answers. Answer: KE = $$\frac{1}{2}$$ mv 2. 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. Accordingly, the kinetic energy increases. K 2 = m.v 2 2 /2, is the final Kinetic energy of the object, and the quantity. You can also get free sample papers, Notes, Important Questions. (i) A force acts on the body. 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. Question 3. Work done = Energy consumed by the lamp = 1000 J Consider the case of an oscillating pendulum. In fact, kinetic energy of an object moving with a certain velocity is equal to the work done to make it acquire that velocity. Q3. In fact, kinetic energy of an object moving with a certain velocity is equal to the work done to make it acquire that velocity. The work done is said to be negative when … Has he done some work or not? Therefore, the work done by gravity on the given object is zero joule. The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. Vertical displacement, h = 0 Q73: (a) Derive an expression to calculate the kinetic energy of a body. 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. Case I Is it a violation of the law of conservation of energy? Hence, Soni is right. Answer : Answer : Question 2 Page 152 - Chapter 11 Class 9 - Work and Energy. Question 2: Write an expression for the kinetic energy of an object. Therefore we can say that kinetic energy is: The derivation of kinetic energy using calculus is given below. 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. Q2 : An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. Q2. Work done by gravity is given by the expression, Work and Energy Class 9 MCQs Questions with Answers. Kinetic Energy: The kinetic energy of an object moving with a certain velocity is the work done on the object to acquire that velocity. Both the methods are explained below. Kinetic energy - The energy possessed by virtue of its motion is said to be kinetic energy. The Questions and Answers of Write an expression for the kinetic energy of an object.? 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. What is the kinetic energy of an object? Heat energy heats the rider’s body. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Displacement, d = 15 m This discussion on Write an expression for the kinetic energy of an object.? Answer: Where K.E. What is its potential energy? Kinetic energy - The energy possessed by virtue of its motion is said to be kinetic energy. Answer : What is its potential energy? In this case, the direction of force acting on the block is perpendicular to the displacement. Question 2 Page 152 - Chapter 11 Class 9 - Work and Energy. Answer: K.E. Substituting in eq n 1, we get, W = 1/2 mv 2. Q2. K 1 =mv 1 2 /2. Hence, 20.8 x 104 J of work is required to stop the car. 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