Q1: For a self-locking machine, the efficiency should be

ANS:A - less than 60%

For a self-locking machine, the efficiency should ideally be less than 60%. Efficiency in this context refers to the mechanical efficiency of the machine, which is the ratio of useful output work to the input work. In the case of a self-locking machine, the mechanism is designed in such a way that it sacrifices some efficiency in exchange for the ability to prevent motion or reverse motion under load without the need for additional mechanisms like brakes. In self-locking mechanisms, part of the input work is used to overcome friction and resistance within the mechanism itself, which can reduce the overall efficiency of the machine. However, this sacrifice in efficiency is acceptable because the primary function of a self-locking machine is to prevent motion or reverse motion without the need for external assistance. Therefore, while the efficiency of a self-locking machine may vary depending on its design and application, it is generally expected to be less than 60% due to the inherent friction and resistance within the mechanism that enable its self-locking capability.