Mechanical Engineering - Online Test
Q1. Atmospheric air at a flow rate of 3 kg/s (on dry basis) enters a cooling and dehumidifying coil with an enthalpy of 85 kJ/ kg of dry air and a humidity ratio of 19 grams/kg of dry air. The air leaves the coil with an enthalpy of 43 kJ/kg of dry air and a humidity ratio of 8 grams/kg of dry air. If the condensate water leaves the coil with an enthalpy of 67 kJ/kg, the required cooling capacity of the coil in kW is
Answer : Option C
Explaination / Solution:
No Explaination.
Q2. A polynomial 
with all coefficients positive has
with all coefficients positive has
Answer : Option D
Explaination / Solution:
Given, the polynomial 
Since, all the coefficients are positive so, the roots of equation is given by
f(x) = 0
It will have at least one pole in right hand plane as there will be least one sign change from (a1) to (a0) in the Routh matrix 1st column. Also, there will be a corresponding pole in left hand plane
i.e.; at least one positive root (in R.H.P)
and at least one negative root (in L.H.P)
Rest of the roots will be either on imaginary axis or in L.H.P
Q3. A ball bearing operating at a load
F has 8000 hours of life. The life of the bearing,
in hours, when the load is doubled to
2F is
Answer : Option D
Explaination / Solution:
No Explaination.
Q4. A heat transformer is device that transfers a part of the heat, supplied to it at an intermediate temperature, to a high temperature reservoir while rejecting the remaining part to a low temperature heat sink. In such a heat transformer, 100 kJ of heat is supplied at 350 K. The maximum amount of heat in kJ that can be transferred to 400 K, when the rest is rejected to a heat sink at 300 K is
Answer : Option D
Explaination / Solution:
No Explaination.
Q5. The solution of the differential equation 
is
is
Answer : Option C
Explaination / Solution:
lny = kx + A
Since y(0) = c thus lnc = A
lny = kx + lnc
Iny = Inekx + Inc
y = cekx
Q6. A model of a hydraulic turbine is tested at a head of 1/4th of that under which the
full scale turbine works. The diameter of the model is half of that of the full scale
turbine. If
N is the RPM of the full scale turbine, the RPM of the model will be
Answer : Option C
Explaination / Solution:
No Explaination.
Q7. Which combination of the following statements is correct ?
The incorporation of reheater in a steam power plant :
P : always increases the thermal efficiency of the plant.
Q : always increases the dryness fraction of steam at condenser inlet
R : always increases the mean temperature of heat addition.
S : always increases the specific work output.
Answer : Option B
Explaination / Solution:
No Explaination.
Q8. The differential equation 100 
describes a system with an
in
put x (t) and an output y(t). The system, which is initially relaxed, is excited by
a unit step input. The output y(t) can be represented by the waveform
describes a system with an
in
put x (t) and an output y(t). The system, which is initially relaxed, is excited by
a unit step input. The output y(t) can be represented by the waveform
Answer : Option A
Explaination / Solution:
100 
Applying Laplace transform we get
Roots are s = 1/10, 1/10 which lie on Right side of s plane thus unstable
Q9. Which combination of the following statements is correct ?
P : A gas cools upon expansion only when its Joule-Thomson coefficient is
positive in the temperature range of expansion.
Q : For a system undergoing a process, its entropy remains constant only when
the process is reversible.
R : The work done by closed system in an adiabatic is a point function.
S : A liquid expands upon freezing when the slope of its fusion curve on
pressure-Temperature diagram is negative
Answer : Option A
Explaination / Solution:
No Explaination.
Q10. A uniformly loaded propped cantilever beam and its free body diagram are shown
below. The reactions are
Answer : Option A
Explaination / Solution:
No Explaination.
