Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): All machines suffer a loss of efficiency due to the frictional force acting on any moving member of the machine.
Reason (R): The frictional force can be reduced by providing a thin film of lubricant between any two parts in contact.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both A and R are correct and R is NOT the correct explanation of A
Assertion (A): All machines suffer a loss of efficiency due to the frictional force acting on any moving member of the machine. Correct. Wherever moving parts rub, friction opposes the motion and turns part of the input work into heat and wear, so the useful output is always less than the input: no real machine is 100% efficient.
Reason (R): The frictional force can be reduced by providing a thin film of lubricant between any two parts in contact. Correct. Oil or grease fills the tiny bumps and hollows of the two surfaces and keeps them apart, so the parts slide over the film instead of over each other.
R does not explain A. A says why machines lose efficiency (friction); R says how friction can be reduced (lubrication). A remedy for the cause is not the reason for the effect.