**Quiz: Mechanical Engineering**

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

**Topic: Miscellaneous**

**Each question carries 4 mark.**

**Negative marking: 1 mark**

**Time: 15 Minute**

Q1. The Coriolis component of acceleration of a slider moving with velocity V on a link having angular velocity ω is

(a) Vω

(b) 2 Vω

(c) 2ω/V

(d) Vω/2

Q2. Weber number is defined as the ratio of

(a) inertia force to viscous force

(b) inertia force to gravity force

(c) inertia force to surface tension force

(d) inertia force to elastic force

Q3. The ratio of RMS value to the average value of an alternating current waveform is called

(a) Peak factor

(b) Power factor

(c) Form factor

(d) None of the above

Q4. Pyrometry deals with the measurement of

(a) Elevated temperature

(b) Shocks

(c) Humidity

(d) Current

Q5. Endurance limit is associated with

(a) Torsion

(b) Bending

(c) Shear

(d) Fatigue

Q6. Which of the following material generally exhibit a yield point?

(a) Cast iron

(b) Annealed and hot rolled mild steel

(c) Soft brass

(d) Glass

Q7. When two springs (of stiffness k each) are in series, then their equivalent stiffness is

(a) k^2

(b) 2k

(c) k/2

(d) 1/k^2

Q8. For a lightly damped vibrating system executing steady state forced vibration, the phase lag of displacement with respect to force at resonance is

(a) 270°

(b) 90°

(c) 45°

(d) 0°

Q9. The center of percussion of a homogeneous uniform rod of length l, pivoted at one end, from the pivot is

(a) (√3/2).l

(b) (2/3).l

(c) (1/√3).l

(d) (√2).l

Q10. The use of draft tube in a reaction turbine helps to

(a) Prevent air from entering in to the turbine

(b) Increase flow rate

(c) Convert kinetic energy in pressure energy

(d) Prevent eddies downstream

**Solutions**

S1. Ans (b)

Sol. The Coriollis component of acceleration is an acceleration of slider moving with velocity V, on a rotating link with angular velocity ω.

i.e. Coriollis component of acceleration =2ωV

It acts on the slider of quick-return motion mechanism.

S2. Ans (c)

Sol. Weber number is defined as the ratio of inertia force to surface tension force. Weber number is applicable for the applications where surface tension force dominates. E.g. Capillary action in a tube etc.

S3. Ans (c)

Sol. The ratio of R.M.S value to the average value of an alternating current waveform is called Form factor.

R.M.S. value of alternating current is (1/√2) times of maximum amplitude of alternating current and average value of alternating current is (2/π) times of maximum amplitude of alternating current.

S4. Ans (a)

Sol. Pyrometry is the branch of science which deals with the measurement of elevated temperatures. Pyrometer is such a device which is used to measure higher temperature (from 300 deg C to 6000 deg C)

S5. Ans (d)

Sol. Endurance limit is defined as the maximum stress/load that a component can sustain without failure when it is being subjected to cyclic loading.

S6. Ans (b)

Sol. Yield point can be exhibited by only ductile material such as annealed and hot rolled

mild steel because of plastic deformation characteristics. Brass is ductile but cannot represent any definite yield point while exhibiting plastic deformation. Cast iron and glass are brittle, so cannot have plastic deformation.

S7. Ans (c)

Sol. When two springs are in series then

Equivalent stiffness (k)=(k1.k2)/(k1+k2)=k/2 (Here, k1=k2=k)

S8. Ans (b)

Sol. For a lightly damped vibrating system executing steady state forced vibration, the phase lag of displacement with respect to force at resonance is 90°.

S9. Ans (b)

Sol. The center of percussion is a point on a pin-supported object where a perpendicular impact will produce no reaction force at the pivot point.

The center of percussion of a homogeneous uniform rod of length l, pivoted at one end, from the pivot is at a distance of (2/3).l

Here, l is length of uniform rod.

S10. Ans (c)

Sol. As there is a loss of pressure head in the reaction turbine at its outlet. To preserve this loss of pressure head, we use draft tube to convert kinetic energy at outlet into pressure energy.