(a) What is meant by static equilibrium? Give one example.

(b) A pulley system has four pulleys in all and is 95% efficient. Calculate

1. MA
2. Effort required to lift a load of 1000 N

(a) When a body remains in a state of rest under the influence of several forces, the body is said to be in static equilibrium.
For example, if a book is lying on a table, the weight of the book exerted on the table vertically downwards is balanced by an equal and opposite force of reaction exerted by the table on the book vertically upwards. Thus, the book is in static equilibrium.

(b) Given,

Efficiency (η) = 95%

Number of pulleys = 4

Velocity ratio = 4 (as the system has 4 pulleys)

MA = ?

We know, $\eta = \dfrac{\text {MA}}{\text {VR}}$

Substituting in the formula above we get,

$\dfrac{95}{100} = \dfrac{\text {MA}}{\text {4}}$

MA = 0.95 x 4 = 3.8

Hence, MA = 3.8

II. From formula : MA = $\dfrac{\text{Load}}{\text{Effort}}$

Substituting in the formula above we get,

3.8 = $\dfrac{1000}{\text{effort}}$

effort = $\dfrac{1000}{3.8}$ = 263.15 N

Hence, effort required = 263.15 N