Question

Fig show a system of four pulleys. The upper two pulleys are fixed and the lower two are movable. 

(i) Draw a string around the pulleys. Also show the place and direction in which the effort is applied.

(ii) What is the velocity ratio of the system?

(iii) What is the mechanical advantage of the system?

(iv) What assumption do you make in arriving at your answer in part (iii)?

Answer 1

(i) Correct winding of rope around pulleys, load and effort is as shown:

(ii) Since there are four strings in the block and tackle system,therefore, velocity ratio of the system is V.R = n = 4.

(iii) M.A = L/E

here, L = 4T, E = T

M.A = `(4"T")/"T" = 4`

(iv) The assumptions made are movable pulleys are weightless and efficiency of the system is 100%.