Question

Name a machine which is used to change the direction of the force.

• A. Lever
• B. Single movable Pulley
• C. Single fixed pulley
• D. Wedge

Answer 1

The correct option is C

Single fixed pulley

A pulley which has its axis of rotation unchanged, is called a fixed pulley.

In equilibrium,

L = T ... (1)

and E = T (when pulley is not rotating) ... (2)

from eqs (1) and (2)

E = L

Mechanical Advantage $=\frac{L}{E}=1$

Thus, in this arrangement there is no gain in the M.A. If the point of application of effort E moves a distance 'd' towards, the load 'L' moves the same distance upwards,

i.e., if $d_E=d$ then $d_L=d$.

$\therefore$ Velocity ratio $=\frac{d_E}{d_L}=\frac{d}{d}=1$

Hence efficiency $n=\frac{M.A}{V.R}=1$ or 100%.

A fixed pulley is used only to change the direction of effort to be applied, i.e, with its use, the effort can be applied in a more convenient direction.