To warm up some milk for a baby, a mother pours milk into a thin-walled cylindrical container whose diameter is 6 cm. The height of the milk in the container is 7 cm. She then places the container into a large pan filled with hot water at 70°C. The milk is stirred constantly so that its temperature is uniform at all times. If the heat transfer coefficient between the water and the container is 120 W/m 2 K, determine how long it will take for the milk to warm up from 3°C to 38°C. Assume the entire surface area of the cylindrical container (including the top and bottom) is in thermal contact with the hot water. Take the properties of the milk to be the same as those of water. Can the milk in this case be treated as a lumped system? Why?
To warm up some milk for a baby, a mother pours milk into a thin-walled cylindrical container whose diameter is 6 cm. The height of the milk in the container is 7 cm. She then places the container into a large pan filled with hot water at 70°C. The milk is stirred constantly so that its temperature is uniform at all times. If the heat transfer coefficient between the water and the container is 120 W/m 2 K, determine how long it will take for the milk to warm up from 3°C to 38°C. Assume the entire surface area of the cylindrical container (including the top and bottom) is in thermal contact with the hot water. Take the properties of the milk to be the same as those of water. Can the milk in this case be treated as a lumped system? Why?
Solution Summary: The author explains that milk can be treated as a lumped system, as the temperature of the milk is assumed to remain constant every time.
To warm up some milk for a baby, a mother pours milk into a thin-walled cylindrical container whose diameter is 6 cm. The height of the milk in the container is 7 cm. She then places the container into a large pan filled with hot water at 70°C. The milk is stirred constantly so that its temperature is uniform at all times. If the heat transfer coefficient between the water and the container is 120 W/m2 K, determine how long it will take for the milk to warm up from 3°C to 38°C. Assume the entire surface area of the cylindrical container (including the top and bottom) is in thermal contact with the hot water. Take the properties of the milk to be the same as those of water. Can the milk in this case be treated as a lumped system? Why?
A crate weighs 530 lb and is hung by three ropes attached to
a steel ring at A such that the top surface is parallel to the
xy plane. Point A is located at a height of h = 42 in above
the top of the crate directly over the geometric center of the
top surface. Use the dimensions given in the table below to
determine the tension in each of the three ropes.
2013 Michael Swanbom
cc00
BY NC SA
↑ Z
C
b
B
У
a
D
Values for dimensions on the figure are given in the following
table. Note the figure may not be to scale.
Variable Value
a
30 in
b
43 in
4.5 in
The tension in rope AB is 383
x lb
The tension in rope AC is 156
x lb
The tension in rope AD is 156
x lb
A block of mass m hangs from the end of bar AB that is 7.2
meters long and connected to the wall in the xz plane. The
bar is supported at A by a ball joint such that it carries only a
compressive force along its axis. The bar is supported at end
B by cables BD and BC that connect to the xz plane at
points C and D respectively with coordinates given in the
figure. Cable BD is elastic and can be modeled as a linear
spring with a spring constant k = 400 N/m and unstretched
length of 6.34 meters.
Determine the mass m, the compressive force in beam AB
and the tension force in cable BC.
Z
C
D
(c, 0, d)
(a, 0, b)
A
B
y
f
m
cc 10
BY
NC SA
2016 Eric Davishahl
x
Values for dimensions on the figure are given in the following
table. Note the figure may not be to scale.
Variable Value
a
8.1 m
b
3.3 m
с
2.7 m
d
3.9 m
e
2 m
f
5.4 m
The mass of the block is 68.8
The compressive force in bar AB is
364
× kg.
× N.
The tension in cable BC is 393
× N.
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