Question

A fire tongs has its arms 20cm long. It is used to lift coal of weight $1.5kgf$ by applying an effort at a distance of 15cm from the fulcrum. Find the effort needed.
A) $0.2kgf$
B) $1.5kgf$
C) $2.5kgf$
D) $2.0kgf$

Answer 1

Hint: Tong is a device that is used to hold or lift things up. It consists of two pieces joined at one end by a common point called the pivot. For example scissors. When a force is applied to an object in order to change its position, it is known as effort. The bulky object that is to be lifted is known as a load.

Complete step by step answer:
Step I:
Given that the length of arms of fire tongs is the load arm on which a load of coal will be lifted.
So, effort arm$ = 20cm$
Effort to lift a coal $ = 1.5kgf$
The distance of the arms of tong from the fulcrum is the load arm $ = 15cm$

Step II:
Machines are designed in a way to manage forces in a way so that movement can be done or the position of objects can be changed. The efficiency of the machines is calculated by their mechanical advantage. It is defined as the ratio of the force created by the machine to the force applied. Here the effort is the force created for the machine and the load is the force applied to lift up the weight of coal. Its formula is
Mechanical advantage $M.A. = \dfrac{{Output\, Force}}{{Input \, Force}}$
$\Rightarrow M.A. = \dfrac{{15}}{{20}}$
$\Rightarrow M.A. = 0.75$
$\Rightarrow \text{Effort} = \dfrac{{Output\,Load}}{{M.A.}}$
$\Rightarrow \text{Effort} = \dfrac{{1.5}}{{0.75}}$
$\Rightarrow \text{Effort} = 2.0kgf$

Therefore, the effort required is $2.0kgf$. Hence, option (D) is the right answer.

Note:
It is important to note that the input force is also called as the effort whereas the output force is also called as load. Also it is important to note that the tong is a type of lever which is also a simple machine. It reduces the amount of force needed to move an object. It makes work easier by spreading the weight to be lifted on its two arms equally.