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sladkih [1.3K]
3 years ago
8

An electric resistance heater is embedded in a long cylinder of diameter 30 mm. when water with a temperature of 25°c and veloc

ity 1 m/s flows crosswise over the cylinder, the power per unit length required to maintain the surface at a uniform temperature of 80°c is 38 kw/m. when air, also at 25°c, but with a velocity of 10 m/s is flowing, the power per unit length required to maintain the same surface temperature is 400 w/m. assume unit length. calculate and compare the convection coefficients for the flows of water and air. according to your calculations, which is a better convective heat transfer media, air or water?
Physics
1 answer:
victus00 [196]3 years ago
3 0
KNOWN: Long, 30mm-diameter cylinder with embedded electrical heater; power required to maintain a specified surface temperature for water and air flows.
 FIND: Convection coefficients for the water and air flow convection processes, hw and ha, respectively.
 ASSUMPTIONS: Flow is cross-wise over cylinder which is very long in the direction normal to flow.
 The convection heat rate from the cylinder per unit length of the cylinder has the form
 q' = h*(pi*D)*(Ts-Tinf)
 and solving for the heat transfer convection coefficient, find
 Water
 hw = q'/((pi*D)*(Ts-Tinf))
 hw = (38*10^3 W/m) / ((pi*(0.030m))*(80-25)C)= 7330.77314  W/m^2K
 Air
 ha = (400W/m) / ((pi*(0.030m))*(80-25)C)=<span> 77.166033 </span> W/m^2K
 COMMENTS: Note that the air velocity is 10 times that of the water flow, yet
hw ≈ 95 × ha.
 These values for the convection coefficient are typical for forced convection heat transfer with liquids and gases
 Watter is a better convective heat transfer media than air 

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Inside a vacuum tube, an electron is in the presence of a uniform electric field with a magnitude of 320 N/C. (a) What is the ma
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(a) The magnitude of the acceleration of the electron is 5.62 x 10¹³ m/s².

(b) The speed of the electron after the given time is  4.78 x 10⁵ m/s.

<h3>Acceleration of the electron</h3>

The acceleration of the electron is calculated as follows;

F = qE

ma = qE

a = qE/m

a = (1.6 x 10⁻¹⁹ x 320)/(9.11 x 10⁻³¹)

a = 5.62 x 10¹³ m/s²

<h3>Speed of the electron</h3>

v = at

v = 5.62 x 10¹³ m/s² x  8.50 x 10⁻⁹ s

v = 4.78 x 10⁵ m/s

Learn more about speed here: brainly.com/question/4931057

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7 0
2 years ago
A BMX bicycle rider takes off from a ramp at a point 2.4 m above the ground. The ramp is angled at 40 degrees from the horizonta
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Answer:

The BMX lands 5.4 m from the end of the ramp.

Explanation:

Hi there!

The position of the BMX is given by the position vector "r":

r = (x0 + v0 · t · cos α, y0 + v0 · t · sin α + 1/2 · g · t²)

Where:

r = position vector at time t

x0 = initial horizontal position

v0 = initial velocity

α = jumping angle

y0 = initial vertical position

g = acceleration due to gravity (-9.8 m/s² considering the upward direction as positive)

Please, see the attached graphic for a better understanding of the situation. At final time, when the bicycle reaches the ground, the vector position will be "r final" (see figure). The y-component of the vector "r final" is - 2.4 m (placing the origin of the frame of reference at the jumping point). With that information, we can use the equation of the y-component of the vector "r" (see above) to calculate the time of flight. With that time, we can then obtain the x-component (rx in the figure) of the vector "r final". Then:

y = y0 + v0 · t · sin α + 1/2 · g · t²

-2.4 m = 0 m + 5.9 m/s · t · sin 40° - 1/2 · 9.8 m/s² · t²

0 = -4.9 m/s² · t² + 5.9 m/s · t · sin 40° + 2.4 m

Solving the quadratic equation:

t = 1.2 s

Now, we can calculate the x-component of the vector "r final" that is the horizontal distance traveled by the bicycle:

x = x0 + v0 · t · cos α

x = 0 m + 5.9 m/s · 1.2 s · cos 40°

x = 5.4 m

The BMX lands 5.4 m from the end of the ramp.

Have a nice day!

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Explanation:

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Assuming South to be negative direction,

From the question,

Total momentum of the two vehicles = (6500-22750)

Total momentum of the two vehicles = -16250 kgm/s

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