**Quiz: Mechanical Engineering**

**Exam: ISRO (TECHNICAL ASST.)**

**Topic: Miscellaneous**

**Each question carries 4 mark.**

**Negative marking: 1 mark**

**Time: 15 Minute**

Q1. Critical speed of a turbine is

(a) Same as runaway speed

(b) Speed that will cause mechanical failure of the shaft

(c) Speed at which natural frequency of vibrations equals the number of revolutions at the same time

(d) Speed equal to synchronous speed of the generator

Q2. A single fixed-point temperature scale is based on

(a) ice point

(b) steam point

(c) triple point of water

(d) critical point of water

Q3. When the fluid flows over the flat plate with a sharp leading edge is examined, laminar flow is generally observed for Reynolds number less than

(a) 2300

(b) 1500

(c) 5×10^5

(d) 1000

Q4. A floating body will be in unstable equilibrium

(a) when its metacentric height is zero

(b) when the metacentre is above center of gravity

(c) when the metacentre is below center of gravity

(d) when the metacentre is at center of gravity

Q5. Mach number is defined as the square root of the ratio of the

(a) inertia force to the pressure force

(b) inertia force to the elastic force

(c) inertia force to the surface tension force

(d) none of these

Q6. The force applied on a body of mass 100 kg to produce an acceleration of 5 m/s^2 is

(a) 500 N

(b) 100 N

(c) 20 N

(d) 10 N

Q7. In case of a circular shaft subjected to torque, the value of shear stress

(a) is uniform through out

(b) has maximum value at axis

(c) has maximum value at the surface

(d) is zero at the axis and linearly increases to a maximum value at the surface of a shaft

Q8. A ball bearing designated by the number 408 is a:

(a) Extra light bearing

(b) Light bearing

(c) Medium bearing

(d) Heavy bearing

Q9. Y-alloy is an alloy of

(a) Nickel

(b) Aluminium

(c) Copper

(d) Tin

Q10. The ultimate tensile strength of low carbon steel by working at high strain rate will

(a) increase

(b) decrease

(c) remain constant

(d) first increase, then decrease

**Solutions**

S1. Ans (c)

Sol. Critical speed of a turbine is the speed of revolutions which is equal to natural frequency of vibration.

S2. Ans (c)

Sol. A single fixed-point temperature scale is based on triple point of water. Triple point of water is that point on P-T diagram at which solid, liquid and vapour phases co-exist together.

S3. Ans (c)

Sol. Flow on a flat plate,

Reynolds number < 5×10^5 (Laminar flow)

Reynolds number > 5×10^5 (Turbulent flow)

S4. Ans (c)

Sol. Metacentric height (distance between metacentre, M and center of gravity, G) decides the stability of a floating body.

If GM > 0 then (Stable)

If GM = 0 then (Neutral)

If GM < 0 then (Unstable)

S5. Ans (b)

Sol. Mach number =√((Inertia Force)/(Elastic Force))

This is applicable for compressible flow.

S6. Ans (a)

Sol. According to Newton’s Second law

F=m.a ………………(1)

Given,

m=100 kg

a=5 m/s^2

From equation (1)

F=100×5

F=500 N

S7. Ans (d)

Sol. When a circular shaft is subjected to torsion then the shear stress will vary according to the following Torsion equation-

T/J=τ/r

τ∝r

So, shear force is zero at the axis and linearly increases to a maximum value at the surface of the shaft.

S8. Ans (d)

Sol. There are following mainly four series of bearings:

1. Extra light (100)

2. Light (200)

3. Medium (300)

4. Heavy (400)

A bearing designated with number 408 then it is used for heavy purposes. This bearing has a bore of 40 mm.

S9. Ans (b)

Sol. Y-alloy is an alloy of aluminium. Other constituents of this alloy are Copper (4%), Nickel (2%), Magnesium (1.5%), Silicon (0.5%) and Iron (0.5%) etc.

S10. Ans (a)

Sol. Ultimate tensile strength of low carbon steel increases when it is worked upon with high strain rate due to increase in number of dislocations in the material.