What does self-locking in a machine mean?
A
The machine locks the user out
B
The machine can operate without effort
C
The machine prevents backward motion even without applying effort
D
The machine runs continuously
Analysis & Theory
Self-locking means the machine prevents the load from moving the effort in reverse due to high friction or design.
Which of the following is a necessary condition for a machine to be self-locking?
A
Efficiency must be 100%
B
Efficiency must be greater than 50%
C
Efficiency must be less than 50%
D
It must use electrical power
Analysis & Theory
For a machine to be self-locking, its efficiency must be less than 50%.
In a self-locking machine, what prevents the load from moving back?
C
High friction in the machine mechanism
Analysis & Theory
High internal friction prevents the load from reversing the direction and moving the effort.
Which of the following machines is commonly designed to be self-locking?
Analysis & Theory
Screw jacks are designed with high friction to be self-locking, ensuring safety under load.
What is the maximum efficiency for a machine to be self-locking?
Analysis & Theory
Machines must have an efficiency of less than 50% to remain self-locking under load.
Why is self-locking important in lifting machines?
C
To ensure the load does not slip back when effort is removed
D
To decrease machine weight
Analysis & Theory
Self-locking is crucial in preventing the accidental return or fall of the load.
Which mechanical condition supports self-locking?
A
Low mechanical advantage
C
High mechanical friction
Analysis & Theory
High friction ensures self-locking by resisting motion reversal under load.
What role does efficiency play in determining self-locking?
A
High efficiency means self-locking
C
Low efficiency helps in self-locking
D
Efficiency must be exactly 50%
Analysis & Theory
Low efficiency (below 50%) is a key requirement for a machine to be self-locking.
Self-locking machines are mostly:
Analysis & Theory
Self-locking machines are inherently irreversible due to high internal resistance to motion reversal.
What happens in a non-self-locking machine when effort is removed?
A
Load stays in place safely
B
Load moves the effort in reverse
D
Machine increases friction automatically
Analysis & Theory
In non-self-locking machines, the load may reverse and move the effort, posing safety risks.