WHAT IS BLOCK AND TACKLE PULLEY SYSTEM , HOW TO FIND THE MECHANICAL ADVANTAGE AND VELOCITY RATIO OF THE SYSTEM ALSO HOW TO FIND EFFICIENCY

Asked by Pushpanjali | 26th Jul, 2016, 09:44: PM

Expert Answer:

BLOCK AND TACKLE: In this system of pulleys, two blocks of fixed pulleys are used. One block (upper) having several fixed pulleys is fixed to a rigid support and the other block (lower) having several fixed pulleys is movable. This is called the block and tackle arrangement.
 
 
The figure shows a block and tackle arrangement of 5 pulleys in which one end of the string is attached to the hook of the lower block.
 
Mechanical advantage: The tension in the five segments (figure a) of the string supports the load L. Therefore, we have
 
begin mathsize 12px style straight L equals 5 straight T
straight E equals straight T end style
 

Therefore, the mechanical advantage is

begin mathsize 12px style straight M. straight A equals straight L over straight E equals 5 end style

In general, if the total number of pulleys used in both the blocks is n and the effort is being applied in the downward direction, then the tension in n segments of the string supports the load, therefore, we have M.A = n.

Velocity ratio: In a block and tackle system if the load moves up through a distance d, the effort end moves through a distance nd because each section of the string supporting the load is loosened by a length d, i.e., if dL = d, then dE = nd.

Therefore, we have

begin mathsize 12px style straight V. straight R equals nd over straight d equals straight n end style


Answered by Romal Bhansali | 27th Jul, 2016, 09:52: AM