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mixer
3 months ago
12

A long plastic rod of 20-mm diameter (k = 0.3 W/m · K and rhocp = 1040 kJ/m3 · K) is uniformly heated in an oven as preparation

for a pressing operation. For best results, the temperature in the rod should not be less than 200°C. To what uniform temperature should the rod be heated in the oven if, for the worst case, the rod sits on a conveyor for 3 min while exposed to convection cooling with ambient air at 25°C and with a convection coefficient of 10 W/m2 · K? A further condition for good results is a maximum–minimum temperature difference of less than 10°C. Is this condition satisfied? If not, what could you do to satisfy it?
Physics
1 answer:
inna [3.1K]3 months ago
6 0

Response:

The temperature required to achieve this is 286.7°C.

Justification:

Provided information:

Diameter = 20 mm = 0.02 m

Le = characteristic length = 0.02/4 = 5x10⁻³m

Thermal conductivity (K) = 0.3 W/m K

Density times specific heat (ρCp) = 1040 kJ/m³ K = 1.04x10⁶

Time (t) = 3 minutes = 180 seconds

Convection heat transfer coefficient (h) = 10 W/m² K

According to transient heat analysis:

\frac{T-25}{T_{o}-25 } =e^{-(\frac{h}{L_{e}\rho Cp } )t}

\frac{200-25}{T_{o} -25} =e^{-(\frac{10}{5x10^{-3}*1.04x10^{6} })*180 } \\T_{o} =272.38C

200°C is the minimum temperature requirement; thus, we assume a value of 210°C (10°C higher) to calculate the necessary temperature:

\frac{210-25}{T_{o} -25} =e^{-(\frac{10}{5x10^{-3}*1.04x10^{6} })*180 } \\T_{o} =286.7C

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A spring is stretched 6 in by a mass that weighs 8 lb. The mass is attached to a dashpot mechanism that has a damping constant o
Ostrovityanka [3204]

Response:

y= 240/901 cos 2t+ 8/901 sin 2t

Clarification:

To determine mass m=weight/g

  m=8/32=0.25

To calculate the spring constant

Kx=mg    (with c=6 inches and mg=8 pounds)

K(0.5)=8               (6 inches converts to 0.5 feet)

K=16 lb/ft

The governing equation for the spring-mass system is

my''+Cy'+Ky=F  

Inserting the known values yields

0.25 y"+0.25 y'+16 y=4 cos 20 t  ----(1) (given C=0.25 lb.s/ft)

Assuming the steady state equation for y is

y=A cos 2t+ B sin 2t

To determine constants A and B, we must equate this with equation 1.

Next, we find y' and y" by differentiating with respect to t.

y'= -2A sin 2t+2B cos 2t

y"=-4A cos 2t-4B sin 2t

Now, substitute the values of y", y' and y into equation 1

0.25 (-4A cos 2t-4B sin 2t)+0.25(-2A sin 2t+2B cos 2t)+16(A cos 2t+ B sin 2t)=4 cos 20 t

By comparing coefficients on both sides

30 A+ B=8

A-30 B=0

From this, we find

A=240/901 and B=8/901

Thus, the steady state response

y= 240/901 cos 2t+ 8/901 sin 2t

6 0
3 months ago
Ceres, Pluto, and Eris are all round in shape and classified as:_________ A) Leftover planetesimals that formed inside the frost
Keith_Richards [3271]

Answer

Ceres, Pluto, and Eris are categorized as DWARF PLANETS.

A) Remaining planetesimals formed within the frost line are referred to as ASTEROIDS.

B) METEORITES are fragments of asteroids that have landed on Earth.

C) COMETS are celestial objects that are often visible with their long tails.

D) COMETS are also planetesimals that were left over and originated in the region of the solar system dominated by the jovian planets.

E) Meteor showers are linked to debris from COMETS.

5 0
3 months ago
THE RELATIVE ANGLE AT THE KNEE CHANGES FROM 0O TO 85O DURING THE KNEE FLEXION PHASE OF A SQUAT EXERCISE. IF 10 COMPLETE SQUATS A
ValentinkaMS [3465]

Answer: total angular distance = 1700° and 29.7 rad

   the total angular displacement = 0

Explanation:

This is a breakdown of the calculations needed.

The task is to determine both the total angular distance and displacement experienced by the knee.

To calculate the distance traveled by the knee, consider that when squatting, the knee bends 85° to lower, and then another 85° to return to standing (upright). Thus, the cumulative angular movement during the squat totals 170°.

For 10 squats, the knee must undergo 170° motion multiplied by 10, resulting in:

10 * 170° = 1700°

As such, the total angular distance reached is 1700°.

Now converting this to radians since both degree and radian outputs are required:

Since 2π equals 360°, it follows that one degree equates to about 57.3°;

∅ (rad) = ∅ (deg) * 2π/360°

∅ (rad) = 1700° * 2π/360° = 29.7 rad

∅ (rad) = 29.7 rad

For the second part, remember that angular displacement is determined by the angular distance divided by time, leading to a displacement of zero because the knee's ending position is the same as its starting position.

I hope this is helpful!!!!

π

5 0
3 months ago
A small block of mass 200 g starts at rest at A, slides to B where its speed is vB=8.0m/s,vB=8.0m/s, then slides along the horiz
serg [3582]

Answer

Data provided:

mass of the block = 200 g = 0.2 Kg

Velocity at A = 0 m/s

Velocity at B = 8 m/s

distance of slide = 10 m

height of the block = 4 m

calculation for the block's potential energy

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    P = 0.2 x 9.8 x 4

    P = 7.84 J

kinetic energy calculated as

    KE = \dfrac{1}{2}mv^2

    KE = \dfrac{1}{2}\times 0.2 \times 7.84^2

    KE =6.14 J

Work done = P - KE

work = 7.84 - 6.14

work = 1.7 J

b) using the formula v² = u² + 2 a s

   0 = 8² - 2 x a x 10

   a = 3.2 m/s²

ma - μ mg = 0

 \mu = \dfrac{a}{g}

 \mu = \dfrac{3.2}{9.8}

 \mu = 0.327

7 0
3 months ago
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