Question

A block and tackle of 5 pulleys is used to raise a load of 50kgf steadily through a height of 20m. Work done against friction is 2000J. Take g=10 ms^-2and calculate
i) Work done by the effort
ii) Efficiency of system
iii) Mechanical advantage

Answer 1

(1) Work done by the effort = work done
against gravity + work done against friction
W = mgh + 2000
= (50 X 10 X 20) + 2000 = 10000 +2000
W = 12000 Joule
(2) Efficiency of system
$\mathit{\eta }\mathbf{}\mathbf{=}\mathbf{}\frac{\mathbf{W}}{\mathbf{m}\mathbf{g}\mathbf{h}}\mathbf{}\mathbf{=}\mathbf{}\frac{\mathbf{12000}}{\mathbf{10000}}\mathbf{}\mathbf{=}\mathbf{}\frac{\mathbf{6}}{\mathbf{5}}$

(3) Mechanical advantage - The ratio of the output force to the input force is the mechanical advantage of takle system .