Question

Observe the figures.

• [(a)] Which one has the mechanical advantage less than one?
• [(b)] State the principle of a lever.
• [(c)] The mechanical advantage of a lever is 2. If the length of its effort arm is 1 m, calculate the length of the load arm.

OR Crowbar can be used as a lever.

• [(a)] What do you mean by a lever?
• [(b)] Among Effort, Load, and Fulcrum, state which one comes in the middle for a second order lever and for a third order lever.
• [(c)] A metre scale is suspended in equilibrium position. If a weight of 60 g is suspended at a distance of 25 cm from the balanced point, what weight must be suspended on the other side at a distance of 30 cm to keep the metre scale in equilibrium?

Hint:

Lever rule: Effort × effort arm = Load × load arm

Answer 1

(A)
(a) Mechanical advantage less than 1
Concept:
Mechanical advantage (MA) less than 1 occurs in third-class levers. Answer:
\[ \text{Figure (iii) (scissors-like tool)} \] (b) Principle of a lever
Principle: \[ \text{Moment of effort} = \text{Moment of load} \] \[ \text{Effort} \times \text{Effort arm} = \text{Load} \times \text{Load arm} \] (c) Calculation of load arm
Step 1: Formula}} \[ \text{MA} = \frac{\text{Effort arm}}{\text{Load arm}} \] Step 2: Given}} \[ \text{MA} = 2,\quad \text{Effort arm} = 1\ \text{m} \] Step 3: Calculation}} \[ 2 = \frac{1}{\text{Load arm}} \Rightarrow \text{Load arm} = \frac{1}{2} = 0.5\ \text{m} \] Conclusion (c): \[ \text{Load arm} = 0.5\ \text{m} \] (B)
(a) Definition of lever
A lever is a rigid bar that rotates about a fixed point called the fulcrum to lift or move a load. (b) Position in levers

• Second order lever → Load is in the middle
• Third order lever → Effort is in the middle

(c) Equilibrium of metre scale
Step 1: Apply principle of moments}} \[ W_1 \times d_1 = W_2 \times d_2 \] Step 2: Given}} \[ W_1 = 60\ \text{g},\quad d_1 = 25\ \text{cm},\quad d_2 = 30\ \text{cm} \] Step 3: Calculation}} \[ 60 \times 25 = W \times 30 \] \[ 1500 = 30W \Rightarrow W = 50\ \text{g} \] Conclusion (c): \[ \text{Required weight} = 50\ \text{g} \]