Mechanical Engineering MCQ Questions and Answers

By Mona Kumari|Updated : June 17th, 2022

Q1. Best fuel for CI engine is

  1. Straight chain paraffin
  2. Aromatics
  3. Branched-chain paraffin
  4. Naphthalene

Answer: A. Straight chain paraffin

Solution:

The best fuel for CI engine is straight chain paraffin, while aromatics are the worst. Aromatics are the best fuel for SI engines, whereas paraffins are the worst. The reason for this is that when utilized in SI engines, regular paraffins have the worst antiknock properties. However, as the quantity of carbon atoms and the molecular structure becomes more compact, the antiknock quality improves. In SI engines, aromatics provide the best knock resistance.

Q2. The shafts are designed on the basis of rigidity and stiffness.

  1. Correct
  2. Incorrect

Answer A. Correct

Solution:

The shafts are designed on the basis of strength or rigidity or both. The goal of a strength-based design is to ensure that stress at any point on the shaft does not exceed the yield stress of the material. The goal of rigidity-based design is to keep the shaft's maximum deflection (due to bending) and maximum twist (due to torsion) within acceptable bounds. In some circumstances, rigidity is also significant. For example, if the shaft is deflected, the position of a gear mounted on the shaft may change, and if this value exceeds some permissible limit, it may cause excessive dynamic loads and noise in the gears.

Q3. Work done in a free expansion process is.

  1. Positive
  2. Negative
  3. Zero
  4. None of the above

Answer: C. Zero

Solution:

Work done in a free expansion process is zero. No external pressure acts on the gas during a free expansion, causing it to expand. The gas expands on its own when no external pressure is applied. The work done during free expansion is little or negligible because the external pressure is zero.

Q4. The friction experienced by a body in motion is known as

  1. Rolling Friction
  2. Dynamic friction
  3. Limiting Friction
  4. Static Friction

Answer - B. Dynamic Friction

Solution:

The friction experienced by a body in motion is known as dynamic friction. The body enters into motion when the force acting on it is greater than the limiting friction. Dynamic friction is the type of friction that now exists between the contact surfaces. The limiting static friction is always less than the dynamic friction.

Q5. Slip of a reciprocating pump is defined as the

  1. Difference of theoretical discharge and actual discharge.
  2. Ratio of actual discharge to theoretical discharge.
  3. Ratio of theoretical discharge to actual discharge.
  4. None

Answer: A. Difference of theoretical discharge and actual discharge.

Solution:

Slip of a reciprocating pump is defined as the difference of theoretical discharge and actual discharge.

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