Question

A crowbar of length 2.0 m is used as a machine, to lift a box of 100 kgf by placing a fulcrum at a distance of 0.1 m from the box. Calculate the (a) V.R. (b) effort required. What assumption has been made by you in solving the problem?

Answer 1

Given: Length of crowbar = 2.0 m; load arm = 0.1 m; load = 100 kgf

\[ \text{Effort arm} = 2.0 - 0.1 = 1.9\ \text{m} \]

(a) Velocity ratio:

\[ \text{V.R.} = \frac{\text{Effort arm}}{\text{Load arm}} \]

\[= \frac{1.9\ \text{m}}{0.1\ \text{m}} \]

\[= 19 \]

(b) Effort required:

\[ \text{M.A.} = \text{V.R.} = 19 \]

\[ \text{M.A.} = \frac{\text{Load}}{\text{Effort}} \]

\[ \therefore \text{Effort} = \frac{\text{Load}}{\text{M.A.}} \]

\[= \frac{100\ \text{kgf}}{19} \]

\[= 5.26\ \text{kgf} \]

Assumption: The crowbar is an ideal machine (efficiency 100%), i.e. it is weightless and there is no loss of energy due to friction, so M.A. = V.R.