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ICSE Class X Notes 2021 : Physics : Machine

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Selina Solutions Concise Physics Class 10 Chapter 3 Machines Exercise 3(A) page no: 57 Question: 1 (a) What do you understand by a simple machine? (b) State the principle of an ideal machine. Solutions: (a) A machine is a device by which we can either overcome a large resistive force (or load) at some point by applying a small force (or effort) at a convenient point and in a desired direction or by which we can obtain a gain in speed. (b) A machine whose parts are weightless and frictionless so that which there is no dissipation of energy in any manner is an ideal machine. The work output is equal to work input i.e its efficiency is 100% Question: 2 State four ways in which machines are useful to us? Solutions: Machines are useful to us in: (a) Lifting a heavy load by applying a less effort (b) Changing the point of application of effort to a convenient point (c) Changing the direction of effort to a convenient direction (d) For obtaining a gain in speed Question: 3 Name a machine for each of the following use: (a) to multiply the force, (b) to change the point of application of force, (c) to change the direction of force, (d) to obtain the gain in speed. Solutions: (a) To multiply the force: a jack is used in lifting a car (b) To change the point of application of force: a cycle s wheel is rotated with the help of a chain by applying the force on the pedal. (c) To change the direction of force: to lift a bucket full of water from the well, a single fixed pulley is used by applying the effort in the downward direction instead of applying it upwards when the bucket is lifted up without the use of pulley. (d) To obtain gain in speed: when a pair of scissors is used to cut the cloth, the blades of a scissors move longer on cloth while its handles move a little. Question: 4 What is the purpose of a jack in lifting a car by it?

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