Question

why the efficiency of a machine can not be 100%​

Answer 1

Explanation:

efficiency of a machine can never be 100%

in a machine, the amount of energy used is always smaller than the amount of energy applied

that is, if the machine is of 1K W, the amount of energy applied must be equal or greater than this and it'll utilize the energy according to its efficiency.

now, it can be said that

what if the efficiency of the machine is 100% so that we could not have any energy wasted?

no matter how flawless the machine is,

it has no control over the gravity through which the earth pulls it. due to the attractive force of the earth towards the machine, some energy is always wasted. for this efficiency can never be 100%