Question

suggest some activities task which illustrate the usefulness of some common machine

Answer 1

Weighing machines can be taken to class and can be informed about its usefulness.  The one which measures the weight of a person and the one that measures the weight of the material  


Wheels – different type of wheels can be shown and its usefulness can be obtained as answers from the students.  


Calculators can be used for stating its uses.   Cycles, screws, hammers, axe etc., are all machines used in our date to date life.

 

Answer 2

You can use the calculator for this purpose. Simple and scientific calculators could be used to show their usefulness

Moreover, a simple weighing would be helpful to show it's usefulness regarding weighing. 
A small wheel could be used to show its benefits. Similarly, scissor is a common machine, you can use it to illustrate its usefulness. 

Also, hammer, bottle openers, and door handles are common examples of machines.

Hope this will help you.