Advertisements
Advertisements
Question
What is a block and tackle system of pulleys? What precautions would you observe while rounding the string so that the effort is applied in the downward direction?
Advertisements
Solution
A block and tackle system of pulleys consists of two blocks of pulleys, each block having one or more than one pulleys. The upper block of pulleys is fixed to a rigid support and the lower block of pulleys is movable. The number of pulleys in the movable block is either equal or one less than the number of pulleys in the fixed block.
While rounding the string, its one end is attached to the hook of the movable block if the number of pulleys in the fixed block is more than that in the movable block or to the hook of the fixed block if the number of pulleys is the same in both the blocks.
RELATED QUESTIONS
A pulley system with VR = 4 is used to lift a load of 175 kgf through a vertical height of 15 m. The effort required is 50 kgf in the downward direction. (g = 10 N kg-1)
Calculate:
- Distance moved by the effort
- Work done by the effort
- M.A. of the pulley system
- Efficiency of the pulley system
The mechanical advantage of an actual pulley is less than one. Give a reason. What is the justification for using the pulley then?
Differentiate between a single fixed pulley and a single movable pulley.
Name a machine to change the direction of force ?
Explain the working of a gear system.
What is a single movable pulley? What is its mechanical advantage in the ideal case?
The diagram below shows a pulley arrangement :
(i) Copy the diagram and mark the direction of tension on each strand of the string.
(ii) What is the velocity ratio of the arrangement ?
(iii) If the tension acting on the string is T, then what is the relationship between T and effort E ?
(iv) If the free end of the string moves through distance x, find the distance by which the load is raised.
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?
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.
