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Chapter 12 - Sound Page no -   163 Solution 1 When the school bell is struck with a hammer, it starts vibrating and as a result of these vibrations, sound is produced by the bell. Solution 2 Sound waves force the medium particles to vibrate. Hence, these waves are known as mechanical waves. Sound waves propagate through a medium because of the interaction of the particles present in that medium. Since the presence of the medium is essential for the sound waves to travel, sound waves are known as mechanical waves. Solution 3 Sound needs a medium to propagate. Since the Moon is devoid of any atmosphere, I will not be able to hear any sound on the Moon. Chapter 12 - Sound Page no -   166 Solution 1 (a) The loudness of a sound is determined by its amplitude. If the amplitude of a sound is large, then the sound produced will also be loud. (b) The pitch of a sound depends on its frequency. A sound will be considered a high pitched sound, if its frequency is ...

Chapter 11 - Work and Energy Page no :-   148 Solution 1 When a force F acts on an object to displace it through a distance s in its direction, then the work done W on the object by the force is given by: Work done = Force × Displacement W = F × s Given: Force, F = 7 N Displacement, s = 8 m   Therefore, work done is, W = F × s W = 7 N × 8 m    = 56 Nm W = 56 J Chapter 11 - Work and Energy Page no :-   149 Solution 1 Work is done whenever the given conditions are satisfied: (i) A force acts on a body. (ii) There is a displacement of the body. Solution 2 When a force F displaces a body through a distance s in the direction of the applied force, then the work done W on the body is given by the expression: Work done = Force × Displacement W = F × s    Solution 3 1 J is the amount of work done by a force of 1 N on an object, to displace it through a distance of 1 ...