Question

A pulley system has 5 pulleys in all and is 90% efficient. If the effort required to lift a load is 1000 N, find the resistance due to the movable parts of machine and friction.

• A. 100 N
• B. 111.1 N
• C. 155.5 N
• D. 2000 N

Answer 1

The correct option is B

111.1 N

Let resistance due to the movable parts of machine and friction = x

Number of pulley, n = 5 = V.R

Efficiency = 90%

M.A = $\eta \times$ V.R

M.A = $\frac{90}{100}$ $\times$ 5 = 4.5

Load = 1000 N

M.A = $\frac{Load}{Effort}$

$\frac{9}{2}$ = $\frac{1000}{E}$

E = $\frac{2000}{9}$ = 222.2 N

M.A = V.R – $\frac{x}{E}$

x = E (V.R – M.A) = $\frac{2000}{9}$ (5 – 4.5) = $\frac{2000}{9}$ $\times$ $\frac{5}{10}$

x = 111.1 N