Advertisements
Advertisements
Question
A ‘block and tackle’ system used 3 pulleys in the lower block and 4 pulleys in the upper block. What is the ‘velocity ratio’ of this system? If the load is to be lifted by a person capable of applying a maximum effort of 1000 N, what is the maximum load than can be lifted under ideal conditions?
The actual maximum load that gets lifted turns out to be 6300 N. What are the values of the actual M.A. and efficiency of the set-up?
Advertisements
Solution
There being 7 pulleys in all, the load is supported by 7 strands of string. Hence it gets lifted only through 1/7 th of the distance through which the effort is applied. Hence the velocity ratio of the setup has a value 7.
Under ideal conditions, M.A. = V.R. = 7
Hence, the maximum load that can be lifted under ideal conditions is:
Effort × 7 = 1000 N × 7 = 7000 N.
Under actual conditions, Load = 6300 N
and Effort = 1000 N
Hence, Actual M.A. =`(6300"N")/(1000"N")=6.3`
Also Efficiency =`"M.A."/"V.R."=6.3/7`
= 0.9 = 90%.
RELATED QUESTIONS
A boy uses a single fixed pulley to lift a load of 50 kgf to some height. Another boy uses a single movable pulley to lift the same load to the same height. Compare the effort applied by them. Give a reason to support your answer.
Is the above pulley system an ideal machine or not?
Differentiate between a single fixed pulley and a single movable pulley.
Define the following term in reference to a gear system for Gain in torque ?
Give reason for the following:
In case of a block and tackle arrangement, the mechanical advantage increases with the increase in the number of pulleys.
Give reason for the following:
The efficiency of a pulley is always less than 100%
Write two uses of pulleys. Is pulley a force multiplier?
There is no gain in mechanical advantage in the case of a single fixed pulley. Explain, why the pulley is then used?
What is the relation between the mechanical advantage and the number of strands of string used to support the load, in a ‘block and tackle’ set-up?
Name the type of single pulley that has an ideal mechanical advantage equal to 2. Draw a labelled diagram of the pulley mentioned by you.
