Question

A crowbar of length 2.5 m is pivoted at a point 25 cm from its tip. Calculate (a) mechanical advantage of crowbar (b) the maximum load displaced by it by applying an effort of 100 kgf on its extreme end.

Answer 1

The crowbar is a lever of the 1st order.

Given: Total length of crowbar = 2.5 m = 250 cm

Load arm = 25 cm

∴ Effort arm = (250 − 25) cm = 225 cm

\[ \text{(a) Mech. advantage} = \text{velocity ratio} = \frac{\text{effort arm}}{\text{load arm}}\]

\[= \frac{225\ \mathrm{cm}}{25\ \mathrm{cm}}\]

= 9

(b) Taking moments about the pivot:

Load × load arm = Effort × effort arm

L × 25 cm = 100 kgf × 225 cm

\[ \therefore\ \mathrm{L} = \frac{100\ \mathrm{kgf} \times 225\ \mathrm{cm}}{25\ \mathrm{cm}}\]

= 900 kgf