The correct answer is: C. More than 50%
A self-locking machine is a machine that can lock itself in place without the need for external assistance. This is achieved by using a mechanism that allows the machine to generate its own power, which is then used to lock the machine in place.
The efficiency of a self-locking machine is the percentage of the input energy that is converted into output energy. A machine with an efficiency of 100% would convert all of the input energy into output energy, while a machine with an efficiency of 50% would convert only half of the input energy into output energy.
In order for a self-locking machine to be effective, it must have an efficiency of greater than 50%. This is because the machine must be able to generate enough power to lock itself in place, even when there is a load on the machine.
If the efficiency of the machine is less than 50%, then the machine will not be able to generate enough power to lock itself in place, and it will not be able to function as a self-locking machine.
Option A: Less than 60%
This option is incorrect because a self-locking machine must have an efficiency of greater than 50% in order to be effective.
Option B: 50%
This option is incorrect because a self-locking machine must have an efficiency of greater than 50% in order to be effective.
Option D: None of these
This option is incorrect because there is one option that is correct.