Deck 3: Introduction to Fluids in Motion

Question 1

The pressure on the lower surface of the cylinder is $20 \mathrm { kPa }$ . If the variation of pressure in the vertical direction is given by $\partial p / \partial z = - 2400 \mathrm {~Pa} / \mathrm { m }$ , the pressure on the upper surface is nearest:
(A) 19.52 kPa
(B) 20.48 kPa
(C) −28.0 kPa
(D) 31.20 kPa

Answer 1

A
A
$19.52 \mathrm { kPa }$
Because the variation is constant, the change in pressure can be written as
$$\Delta p = \frac { \partial p } { \partial z } \Delta z = - 2400 \mathrm {~Pa} / \mathrm { m } \times 0.2 \mathrm {~m} = - 480 \mathrm {~Pa} . \quad \therefore p _ { \text {upper } } = 20 - 0.48 = \underline { 19.52 \mathrm { kPa } }$$

Question 2

The force shown is partially due to a pressure acting uniformly over the area of 100 cm2. The pressure is nearest:

A) 6.02 kPa
B) 6.91 N·m
C) 8.84 N·m
D) 10.1 N·m

Answer 2

10.1 N·m

Question 3

A water-well driller measures the water level in a well to be 20 ft below the surface. The point on the well is 250 ft below the surface. The pressure at the point, in SI units, is estimated to be:

A) 632 kPa
B) 652 kPa
C) 688 kPa
D) 698 kPa

Answer 3

688 kPa

Question 4

The percentage error, considering the pressure from Table B.3 in the Appendix to be more accurate, is nearest:

A) 0.08 %
B) 0.13 %
C) 0.24 %
D) 0.31 %