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Tensioneach strand.18. Give reasons for the following:(a) In a single fixed pulley, the velocity ratio isalways more than the mechanical advantage.(b) The efficiency of a movable pulley is alwaysless than 100%.(c) In case of a block and tackle system, themechanical advantage increases with theincrease in the number of pulleys.(d) The lower block of a block and tackle pulleysystem must be of negligible weight. |
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Answer» Answer: Explanation:(a) In a single fixed PULLEY, some effort is wasted in OVERCOMING friction between the strings and the grooves of the pulley; so the effort needed is greater than the LOAD and hence the mechanical advantage is less than the velocity ratio. (b) This is because of some effort is wasted in overcoming the friction between the strings and the grooves of the pulley. (c) This is because mechanical advantage is equal to the total number of pulleys in both the blocks. (d) The efficiency depends upon the mass of lower block; THEREFORE efficiency is reduced DUE to the weight of the lower block of pulleys. |
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