A screw jack used for lifting the load is

55) For a self locking machine, the efficiency must be

Answer is:

less than 50 percent

Explanation:

Reversible machine If a machine is capable of doing some work in the reversed direction, after the effort is removed, then the machine is known as reversible machine. The condition for a machine to be reversible is that its efficiency should be more than 50 %.
Non- reversible or self locking machine If a machine is not capable of doing some work in the reversed direction, after the effort is removed, then the machine is known as non-reversible or self locking machine. The condition for a machine to be non-reversible or self locking is that its efficiency should be less than 50 %.

56) Which of the following statement is wrong?

A force acting in the opposite direction to the motion of the body is called force of friction.

The ratio of the limiting friction to the normal reaction is called coefficient of friction.

A machine whose efficiency is 100 percent is known as an ideal machine.

The velocity ratio of a machine is the ratio of load lifted to the effort applied.

Answer is:

The velocity ratio of a machine is the ratio of load lifted to the effort applied.

Explanation:

Velocity ratio of a machine is the ratio of load lifted to the effort applied.

57) If the number of pulleys in a system is equal to its velocity ratio, then it is a ______system of pulleys

Answer is:

second

Explanation:

58) The velocity ratio of a single purchase crab winch can be increased by

increasing the length of the handle

increasing the radius of the load drum

increasing the number of teeth of the pinion

all of the above

Answer is:

increasing the length of the handle

Explanation:

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A screw jack used for lifting the load is

a non-reversible machine

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Related Engineering Mechanics MCQ with Answers

55) For a self locking machine, the efficiency must be

less than 50 percent

56) Which of the following statement is wrong?

The velocity ratio of a machine is the ratio of load lifted to the effort applied.

57) If the number of pulleys in a system is equal to its velocity ratio, then it is a ______system of pulleys

second

58) The velocity ratio of a single purchase crab winch can be increased by

increasing the length of the handle

For More Engineering Mechanics MCQ with Answers