Physics 131 Test/Exam Problems: Fluids
1) What is the difference in blood pressure between the head and bottom of the feat
for a person of height 1.6 m? (16, 600 Pa) (blood = 1060 kg/m3)
2) A wooden board 9 cm thick floats in water with its upper surface parallel to the
waters surface. If the upper 3.5 cm of the board is above the water, estimate the
density of the board. (611 kg/m3) (water = 1000 kg/m3)
3) What is the force on your roof if the wind blows over it with a speed of 30 m/s.
Assume the area of your roof is 240 m2. (1.4  105 N) The density of air is 1.29
kg/m3.
4) A slab of ice (density = 920 kg/m3, volume = 0.725 m3) floats on a freshwater
lake. What is the maximum mass that a woman can have in order that she can
stand on the ice without getting her feet wet? (58 kg)
5) The pressure on the roof of a tall building is 0.993 × 105 Pa and the pressure on
the ground is 1.010 × 105 Pa. The density of air is 1.29 kg/m3. What is the height
of the building? (135 m)
6) A hydraulic lift is used to lift a block of mass M. The block rests on the right
massless plunger. A force F1 is applied to the left massless plunger. The two
plungers are at the same height. The diameter of the left cylinder is D1 and the
diameter of the right cylinder is D2. What force F1 is required to lift the block? (d)
(a)
(b)
(c)
(d)
(e)
Mg
Mg(D1/D2)
Mg(D2/D1)
Mg(D1/D2)2
Mg(D2/D1)2
7) A square block of side 6.3 cm that is tethered by a string floats in water in a tank.
See figure.
Suppose the tension in the string is T = 0.5 N. What is the density of the floating mass
m? (e)
(a)
(b)
(c)
(d)
(e)
344 kg/m3
419 kg/m3
501 kg/m3
699 kg/m3
797 kg/m3
8) Suppose the water in the tank is 1.3 m deep. How much greater is the pressure at
the bottom than at the top? (e)
(a)
(b)
(c)
(d)
(e)
980 Pa
1402 Pa
3870 Pa
8880 Pa
12740 Pa
9) Consider blood (density 1025 kg/m3) flowing through an artery with circular cross
section that looks like this:
10) What is the mass flow rate in this artery? Ignore viscosity. Assume that the
change in height is negligible between regions A, B, and C. (b)
(a)
(b)
(c)
(d)
(e)
0.011 kg/s
0.024 kg/s
0.039 kg/s
0.052 kg/s
0.128 kg/s
11) What is the difference PB - PA in the pressure between region B and region A? (a)
(a)
(b)
(c)
(d)
(e)
+46 Pa
+13 Pa
0 Pa
-13 Pa
-46 Pa