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Fluid Mechanics and Hydraulic Machinery Miscellaneous

Fluid Mechanics and Hydraulic Machinery

  1. Water flows though a pipe with a velocity given by V =
    4
    + x + y ĵ m/s
    t

    m/s, where ĵ is the unit vector in the y direction, t(>0) is in seconds, and x and y are in meters. The magnitude of total acceleration at the point (x, y) = (1, 1) at t = 2 s is _____ m/s².
    1. 3 m/s²
    2. 29 m/s²
    3. 10 m/s²
    4. 30 m/s²
Correct Option: A

Given:

V =
4
+ x + y ĵ m/s
t

V = uî + vĵ + wk̂
u = 0, w = 0
V =
4
+ x + y
t

a = axî + ayĵ + az
ax = u
∂u
+ v
∂u
+ w
∂u
+
∂u
= 0
∂x∂y∂z∂t

az = u
∂w
+ v
∂w
+ w
∂w
+
∂w
∂x∂y∂z∂t

ay = u
∂v
+ v
∂v
+ w
∂v
+
∂v
∂x∂y∂z∂t

= u
∂v
+ v
∂v
∂y∂t

=
4
+ x + y × 1 +
4
t

ay =
4
+ x + y −
4
t

Now, At (x,y) = 1,1 and t = 2 sec.
Total acceleration is given by,
a = ay =
4
+ 1 + 1 −
4
= 3 m/s²
24



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