Question

A man uses a crowbar of length $2.5\text{m}$ to raise a load of $75\text{kgf}$ by putting a sharp edge below the bar at a distance $1\text{m}$ from his hand. State the kind of lever used and calculate the effort needed.

• A. Class $\text{II}$ lever, $35\text{kgf}$
• B. Class $\text{I}$ lever, $35\text{kgf}$
• C. Class $\text{I}$ lever, $50\text{kgf}$
• D. Class $\text{III}$ lever, $37.5\text{kgf}$

Answer 1

The correct option is C Class $\text{I}$ lever, $50\text{kgf}$

Load arm $=2.5–1.0=1.5\text{m}$

Effort arm $=1\text{m}$

Mechanical Advantage $=\frac{1.5}{1}=1.5$

Mechanical Advantage $=\frac{\text{Load}}{\text{Effort}}$

$1.5=\frac{75\text{kgf}}{E}$

$E=\frac{75}{1.5}=50\text{kgf}$

Since fulcrum lies in between so it belongs to Class $\text{I}$ Lever.