(i) A force acts on the body. Work done = Energy consumed by the heater Work is done whenever the given two conditions are satisfied: Kinetic energy is given by the expression, The work done is said to be negative when … = where m = mass of the object and v = uniform velocity of the object. Answer : 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”. v 2 = 2as. 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. Kinetic energy - The energy possessed by virtue of its motion is said to be kinetic energy. Think. Therefore, work done, W= 7 ÃƒÆ’Ã¢â‚¬”8 at rest, u=0. Thus equation (i) becomes. Write an expression for the kinetic energy of an object. (i) Kinetic energy when the object was moving with a velocity 5 m s -1 h= Vertical displacement = 0 How much energy is this in joules? 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. The net force acting on it is zero. 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. 2. Answer : Work done = Force ÃƒÆ’Ã¢â‚¬”Displacement Vertical displacement is given by the difference in the initial and final positions/heights of the object, which is zero. Kinetic energy when the object was moving with a velocity 2 m s −1. is done on EduRev Study Group by Class 9 Students. Moreover, this energy should be either a zero or a negative value. Power is given by the expression, What will be its kinetic energy when its velocity is doubled? Where, All NCERT textbook questions have been solved by our expert teachers. The kinetic energy of an object of mass, m moving with a velocity of 5 m s–1 is 25 J. Q13 : A person holds a bundle of hay over his head for 30 minutes and gets tired. = 56 Nm 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: A body uses kinetic energy to do work. Since work done is stored in kinetic energy. Work done by force is equal to the change in kinetic energy. m= Mass of the object (b) An object of mass 70 kg is raised to a height of 10 metres above the ground. Answer : derive equation for loss of kinetic energy in case of a completely inelastic collision in one dimension - Physics - TopperLearning.com | 98uzboee Work done by gravity depends only on thevertical displacement of the body. • An engine is pulling a train. Accordingly, the kinetic energy increases. Kinetic energy is the energy possessed by an object because of motion. 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. Answer : Calculate the work done by the force. Your email address will not be published. Applied force, F = 140 N Acceleration in an object could be zero even when several forces are acting on it. Case III. W = mg x 0 = 0 J 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. What will be its kinetic energy when its velocity is doubled? If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? v is the velocity with which body is moving. Obtain an expression for the kinetic energy of an object. Answer : Hence, the acceleration of the object is zero. Q8 : Write an expression for the kinetic energy of an object. This energy is dependent on the velocity of the object squared. Hence, work is done by Seema while swimming. 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. The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. ... 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 - … Work done by gravity is given by the expression, = Kinetic energy of the object moving with a velocity, v Discuss this question with your friends and teacher. Question 7. Work and Energy CBSE Class 9 Science Chapter 11 - Complete explanation and Notes of the chapter ‘Work and Energy’.. Therefore, energy consumed = Power x Time 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 […] Write an expression for the kinetic energy of an object. 11.3). Write an expression for the kinetic energy of an object. 7)A falling coconut, running athlete possesses kinetic energy. Q3 : When do we say that work is done? It comes to rest because air resistance resists its motion. This discussion on Mathematical expression of kinetic and potential energy is done on EduRev Study Group by Class 9 Students. What is its potential energy? Answer : What is the kinetic energy of an object? Q72: Define kinetic energy. Reason out whether or not work is done in the light of your understanding of the term ‘work’. Therefore, the work done by gravity on the given object is zero joule. Why does the bob eventually come to rest? m is the mass of the body. Question 2 Page 152 - Chapter 11 Class 9 - Work and Energy. Where, Work and Energy Kinetic Energy . For a uniformly moving object S= 8 m SOLUTION: Kinetic energy of an object, where m = mass of the object and v = uniform velocity of the object. W= 140 x 15 = 2100 J Case I Therefore, there is a displacement in the train in the same direction. Therefore, its kinetic energy becomes 4 times its original value, because it is proportional to the square of the velocity. A body can do different amount of work in different time intervals. 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. (ii) There is a displacement of the body by the application of force in or opposite to the direction of force. Q7 : What are the various energy transformations that occur when you are riding a bicycle? Velocity of car, v= 60 km/h 1 kWh = 3.6 x 106 J Download free PDF of best NCERT Solutions , Class 9, Physics, CBSE- Work and Energy . The kinetic energy of a body is the energy possessed by the body by virtue of its motion. Energy consumed by an electric heater can be obtained with the help ofthe expression, Write an expression for the kinetic energy of an object. Q2 : An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. 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. Answer : "Energy posses by a body by virtue of its motion is referred to as 'Kinetic Energy'". MCQ Questions for Class 9 Science with Answers were prepared based on the latest exam pattern. Hence, kinetic energy = 25 x 4 = 100 J. As the object touches the ground, all its potential energy gets converted into kinetic energy. Q9 : A certain household has consumed 250 units of energy during a month. Kinetic energy is the energy possessed by an object because of motion. Kinetic energy when the object was moving with a velocity 2 m s −1. Therefore, there is a displacement in the boat in the direction of force. The kinetic energy of an object of mass, m moving with a velocity of 5 ms-1 is 25 J. K 2 = m.v 2 2 /2, is the final Kinetic energy of the object, and the quantity. SOLUTION: Kinetic energy of an object, where m = mass of the object and v = uniform velocity of the object. It is further classified into gravitational potential energy (GPE) and elastic potential energy … The pendulum loses its kinetic energy to overcome this friction and stops after some time. Where, This theorem states that the net work on a system goes into kinetic energy. Students must understand the kinetic energy derivation method properly to excel in their examination. The process does not violate the law of conservation of energy. Work, Power And Energy Class 9 Extra Questions Short Answer Type 2. 13.4k LIKES. Exercise : Solutions of Questions on Page Number : 158. For a uniformly moving object, the net force acting on the object is zero. Mass of car, m= 1500 kg Q12 : Can there be displacement of an object in the absence of any force acting on it? is the kinetic energy. The energy possessed by a body by virtue of its motion is called kinetic energy. Your email address will not be published. (b) While carrying a load, the donkey has to apply a force in the upward direction. W= F x d Q9 : The kinetic energy of an object of mass, m moving with a velocity of 5 m s-1  is 25 J. Yes. Solution: Kinetic energy of an object, K.E. The derivation of kinetic energy is one of the most common questions asked in the examination. Physics. Classically, kinetic energy is related to mass and speed by the familiar expression K = 1 2 m u 2. The corresponding relativistic expression for kinetic energy can be obtained from the work-energy theorem. Substituting in eq n 1, we get, W = 1/2 mv 2. 15.6k VIEWS. 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: This process is repeated as long as the pendulum oscillates. Question 2: Write an expression for the kinetic energy of an object. Kinetic energy is a property of a moving object or particle and depends not only on its motion but also on its mass. Work, Power And Energy Class 9 Extra Questions Short Answer Type 2. Where, The kinetic energy of an object of mass, m moving with a velocity of 5 m s-1 is 25 J. Hence, Soni is right. (b) If the velocity of an object is doubled. Answer : =40-250 = -210 J The kind of motion may be translation, rotation about an axis, vibration, or any combination of motions. Work done = Energy consumed by the device 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? (i) A force acts on the body. Required fields are marked *. Therefore, Suma swims in the forward direction caused by the forward reaction of water. Q6 : A pair of bullocks exerts a force of 140 N on a plough. (i) A force acts on the body. Work done by force is equal to the change in kinetic energy. Hence, it is better to define average power. This discussion on Mathematical expression of kinetic and potential energy is done on EduRev Study Group by Class 9 Students. (ii) There is a displacement of the body caused by the applied force along the direction of the applied force. Given that kinetic energy, = 25 J Answer : F= 7 N Work done by the force of gravity on an object depends only on vertical displacement. at rest, u=0. are solved by group of students and teacher of Class 9, which is also the largest student community of Class 9. Let us take it that the force acts on the object through the displacement. (a) While swimming, Suma applies a force to push the water backwards. Derivation : We know that, W = f x s but f = ma. Question 8. • Suma is swimming in a pond. Q14 : An electric heater is rated 1500 W. How much energy does it use in 10 hours? Answer : Q3. 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, v 2 = 2as. If the direction of force is perpendicular to displacement, then the work done is zero. Answer : (b) An object of mass 70 kg is raised to a height of 10 metres above the ground. 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. Write an expression for the kinetic energy of an object. Work done = Force x Displacement W = mas ….. (1) By 3 rd eq n of motion, v 2 = u 2 + 2as. Why? Since, displacement is perpendicular to force, the work done is zero. Write an expression for the kinetic energy of a body of mass m moving with a velocity v. work and energy; class-9; Share It On Facebook Twitter Email. Q72: Define kinetic energy. = 1.5 x 10 = 15 kWh Q7 : What is the kinetic energy of an object? The kinetic energy of a body is the energy that it possessed due to its motion. Answer: Every moving object possesses kinetic energy. Therefore, work done by gravity is given by the expression, (ii) Kinetic energy when the object was moving with a velocity 2 m s-1 Timefor which the heater has operated, T= 10 h Answer : Work, Power And Energy Class 9 Extra Questions Short Answer Questions-II. Hence, work is done by the wind mill in lifting water from the well. K E = 1/2mv 2. 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. Q21 : A freely falling object eventually stops on reaching the ground. ∴W= mg x 0 = 0 Unit of Energy: Unit of energy is same as that of the unit of work. Q 8. (f) Food grains do not move in the presence of solar energy. Therefore we can say that kinetic energy is: Derivation of Kinetic Energy using Calculus. What is the work done by the force of gravity on the object? The bob does not oscillate forever. as = 1/2 v 2. Hence, the work done by gravity on the body is zero. Q5 : A mass of 10 kg is at a point A on a table. Sol. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero. So the kinetic energy at rest should be zero. What will be its kinetic energy when its velocity is doubled? Hence, in the absence of force, work done by the person on the bundle is zero. What is the kinetic energy of an object? (i) A force acts on the body. The energy possessed by a body by virtue of its motion is called kinetic energy. = ½ mv 2. If the velocity of the body is zero, then the kinetic energy will also be zero. Kinetic energy can be defined as the work needed to accelerate an object of a given mass from rest to its stated velocity. As the object hits the hard ground, all its kinetic energy gets converted into heat energy and sound energy. Time for which the device runs, T= 10 h W=K 2-K 1 =ΔK-----(ii) Where, ΔK = change in KE of the object. 1 unit = 1 kWh ... 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. Hence, 2100 J of work is done in ploughing the length of the field. Answer: KE = $$\frac{1}{2}$$ mv 2. Write an expression for the kinetic energy of an object. Objects in motion possess energy, we call this energy kinetic energy. Is it a violation of the law of conservation of energy? Q3. 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