Question

A man applies the effort of 150 N on one end of a fixed pulley to pull a bucket of water of mass 12 kg. What is the force of friction, mechanical advantage and efficiency of this pulley?

Answer 1

Given:

Effort (E) = 150 N

Mass of the bucket (m) = 12 kg

Acceleration due to gravity (g) = 10 m/s²

Load (L) = m × g

= 12 × 10

= 120 N

For a single fixed pulley, the standard Velocity Ratio (VR) is always 1.

(i) In a single fixed pulley with friction, the effort applied must overcome both the load and the frictional force:

E = L + f

150 = 120 + f

f = 150 − 120

f = 30 N

(ii) Mechanical Advantage (MA) = `"Load (L)"/"Effort (E)"`

= `120/150`

= 0.8

(iii) Efficiency (η) = `(MA)/(VR) xx 100%`

= `0.8/1 xx 100%`

= 80%

The force of friction is 30 N, the mechanical advantage is 0.8, and the efficiency is 80%.