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Water flows in a streamline motion through a horizontal pipe of circular cross-section as shown in the figure. The pressure difference of water between P and Q is 15Nm−2. The area of cross-section at P and Q are 40cm2 and 20cm2, respectively. The rate of flow of water through the pipe, in cm3s−1, is:
[Take density of water =1000kgm−3]
A.
400
✓
B.
100
C.
200
D.
300
Answer:A
Since the fluid is incompressible and flows through a pipe of varying cross-section, the continuity equation applies, meaning the volume flow rate stays the same at P and Q.
APVP=AQVQ
Given the areas, so
40VP=20VQ⟹VQ=2VP
Since the pipe is horizontal, Bernoulli's equation relates the pressure difference to the change in velocity.
PP−PQ=21ρ(VQ2−VP2)
Substituting the given values,
15=21×1000×(4VP2−VP2)
Solving this equation gives the velocity at P.
VP=150015=0.1m/s
Therefore
VQ=0.2m/s
The rate of flow through the pipe equals APVP.
Rate=40×10−4×0.1=4×10−4m3/s
Converting to cm3/s,
4×10−4×106=400cm3/s
Hence, the answer is A. 400.
Q2 · 2026
In the measurement of viscosity of liquids using terminal velocity experiment, spherical balls of same radius but having different densities are used. The variation of the terminal velocity ( v ) with the ratio of density of spherical ball ( σ ) to density of the liquid ( ρ ), is best represented by:
A.
B.
✓
C.
D.
Answer:B
Recall the expression for terminal velocity from Stokes' law, where r is the radius of the ball, h is the coefficient of viscosity, σ is the density of the ball, and ρ is the density of the liquid.
VT=9h2r2(σ−ρ)
To compare VT with ρσ, rewrite the expression by factoring out ρ.
VT=9h2r2ρ(ρσ−1)
This has the same form as the equation of a straight line, where y=VT, x=ρσ, the slope m=9h2r2ρ is positive, and the intercept c=−9h2r2ρ is negative.
y=mx+c
A positive slope with a negative intercept means the graph is a straight line that crosses the x-axis (at ρσ=1) and increases afterward.
Hence, the answer is B.
Q3 · 2026
Match List I with List II:
List I
List II
A.
Young's Modulus
I.
ΔLΔd(dL)
B.
Compressibility
II.
A(ΔL)FL
C.
Bulk Modulus
III.
−ΔP1(VΔV)
D.
Poisson's Ratio
IV.
−P(ΔVV)
Choose the correct answer from the options given below:
A.
A-IV, B-I, C-II, D-III
B.
A-III, B-II, C-I, D-IV
C.
A-I, B-IV, C-III, D-II
D.
A-II, B-III, C-IV, D-I
✓
Answer:D
Young's Modulus is defined as the ratio of longitudinal stress to longitudinal strain.
Y=AΔLFL
So A matches II.
Compressibility is the reciprocal of Bulk Modulus.
Compressibility=−ΔP1(VΔV)
So B matches III.
Bulk Modulus is defined as negative of the pressure change divided by the fractional volume change.
K=−P(ΔVV)
So C matches IV.
Poisson's Ratio is defined as lateral strain divided by longitudinal strain.
μ=ΔLΔd(dL)
So D matches I.
Hence, the correct matching is A-II, B-III, C-IV, D-I, so the answer is D.