**Quiz: Mechanical Engineering**

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

**Topic: Miscellaneous**

**Each question carries 4 mark.**

**Negative marking: 1 mark**

**Time: 15 Minute**

Q1. Higher critical temperature of steel is

(a) 950℃

(b) 1560℃

(c) 800℃

(d) 723℃

Q2. Which of the following represents Reynolds number?

(a) Ratio of thermal conductivity to kinematic viscosity

(b) Ratio of inertia force to viscous force

(c) Ratio of heat convected to heat conducted

(d) None of these

Q3. If degree of superheat is increased in vapour compression refrigeration cycle then

(a) Refrigeration effect decreases

(b) Refrigeration effect increases

(c) Work input of compressor decreases

(d) None of these

Q4. When the Mach number is more than unity, then the flow is

(a) Supersonic

(b) Sonic

(c) Subsonic

(d) None of the above

Q5. The moment of inertia of a circular section of diameter D about its polar axis is________the moment of inertia about its diameter.

(a) four times

(b) double

(c) three times

(d) half

Q6. Which of the following type of tool is used in the ultrasonic machining process?

(a) Glass

(b) Cast iron

(c) Brass

(d) Diamond

Q7. Which of the following can be used to reduce interference between two involute gears?

(a) Increase width of the gear teeth

(b) Increase center distance between gears

(c) Decrease pressure angle

(d) None of these

Q8. The heat that must be absorbed by ice of mass 1 kg at -5℃ to take it to water at 10℃ is (specific heat of ice is 2.1 kJ/kg-K, specific heat of the water is 4.2 kJ/kg-K and latent heat of fusion of ice is 310kJ/kg)

(a) 363 kJ

(b) 243 kJ

(c) 192 kJ

(d) 203 kJ

Q9. There are five numbers 3, 4, 5, 7 and 8. The average value and root mean square value of these numbers are

(a) 13, 5

(b) 13.5, 5.7

(c) 5.7, 13.5

(d) 4, 5

Q10. Which of the following is valid condition for maximum power transmission in a belt?

(a) Total tension is equal to centrifugal tension

(b) Total tension is 2π times centrifugal tension

(c) Total tension is thrice the centrifugal tension

(d) Total tension is half the centrifugal tension

**Solutions**

S1. Ans (a)

Sol. Higher critical temperature of steel is 925℃ and lower critical temperature of steel is 723℃.

S2. Ans (b)

Sol. Reynolds Number(Re)=(Inertia Force)/(Viscous Force)=ρVd/μ

Here,

ρ=Density of fluid

V=Average velocity of fluid

d=Diameter of conduit

μ=Dynamic viscosity of fluid

S3. Ans (b)

Sol. As degree of superheat is increased in vapour compression refrigeration cycle then refrigeration effect and work input to compressor both increases.

S4. Ans (a)

Sol.

1. If Mach Number (Ma<1) then flow is subsonic.

2. If Mach Number (Ma=1) then flow is sonic.

3. If Mach Number (Ma>1) then flow is supersonic.

4. If Mach Number (Ma>3) then flow is hypersonic.

S5. Ans (b)

Sol.

Moment of inertia about the diameter=(πD^4)/64

Moment of inertia about polar axis=(πD^4)/32

S6. Ans (c)

Sol. For ultrasonic machining, we use tool of ductile material which can embed brittle abrasive slurry within itself.

S7. Ans (b)

Sol. There are following ways to reduce interference between gears.

1. Use of larger pressure angle

2. Increase in center distance

3. Tooth stubbing

4. Increasing number of teeth on gears keeping diameter same

S8. Ans (a)

Sol. Heat absorbed by ice at -5℃ to convert into water 10℃ = heat taken by ice from -5℃ to 0℃ + heat taken for phase change of ice into water at 0℃ + heat taken by water from 0℃ to 10℃

=1×2.1×(0-(-5)+1×310+1×4.2×(10-0)

=362.5 kJ

S9. Ans (b)

Sol.

Average value=(Sum of elements)/(Total number of elements)=(3+4+5+7+8)/5=13.5

Root mean square value=√((3^2+4^2+5^2+7^2+8^2)/5)=5.7

S10. Ans (c)

Sol.

For maximum power transmission in a belt,

Total tension in the belt (T) = 3 × Centrifugal Tension (Tc)