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3 years ago

An HVAC contracting company sent out three work crews to complete three

Engineering

1 answer:

Doss [256]3 years ago

6 0

Answer: 156 hours

Explanation:

Crew One worked 10-, 9-, 11-, 12-, and 9-hours for the week. The total hours worked by Crew One will be:

= 10 + 9 + 11 + 12 + 9

= 51 hours.

Crew Two worked 9, 12, 12, 9 and 9 hours. The total hours worked by Crew Two for the week will be:

= 9 + 12 + 12 + 9 + 9

= 51 hours

Crew Three worked 12-, 12-, 10-, 9-, and 11-hour daily. The total hours worked by Crew Three for the week will be:

= 12 + 12 + 10 + 9 + 11

= 54 hours

The total hours worked by the three crews for the week will be:

= 51 hours + 51 hours + 54 hours

= 156 hours

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The production process of rods from machine "A" yields specimen with the following specs. Mean: µ(LA)=20.00mm, STD: s(LA)=0.50mm

Oxana [17]

Answer: the standard deviation STD of machine B is s (Lb) = 0.4557

Explanation:

from the given data, machine A and machine B produce half of the rods

Lt = 0.5La + 0.5Lb

s² (Lt) = 0.5²s²(La) + 0.5²s²(Lb) + 0.5²(2)Cov (La, Lb)

but Cov (La, Lb) = Corr(La, Lb) s(La) s(Lb) = 0.4s (La) s(Lb)

so we substitute

s²(Lt) = 0.25s² (La) + 0.25s² (Lb) + 0.4s (La) s(Lb)

0.4² = 0.25 (0.5²) + 0.25s² (Lb) + (0.5)0.4(0.5) s(Lb)

0.64 = 0.25 + s²(Lb) + 0.4s(Lb)

s²(Lb) + 0.4s(Lb) - 0.39 = 0

s(Lb) = { -0.4 ± √(0.16 + (4*0.39)) } / 2

s (Lb) = 0.4557

therefore the standard deviation STD of machine B is s (Lb) = 0.4557

8 0

3 years ago

Refrigerant-134a at 700 kPa, 70°C, and 7.2 kg/min is cooled by water in a condenser until it exists as a saturated liquid at the

alex41 [277]

Answer:

The mass flow rate of cooling water required to cool the refrigerant is $123.788\,\frac{kg}{min}$ .

Explanation:

A condenser is a heat exchanger used to cool working fluid (Refrigerant 134a) at the expense of cooling fluid (water), which works usually at steady state. Let suppose that there is no heat interactions between condenser and surroundings.The condenser is modelled after the First Law of Thermodynamics, which states:

$\dot Q_{ref} - \dot Q_{w} = 0$

$\dot Q_{ref} = \dot Q_{w}$

$\dot m_{ref}\cdot (h_{ref, in} - h_{ref,out}) = \dot m_{w}\cdot (h_{w, out} - h_{w,in})$

The mass flow rate of the cooling water is now cleared:

$\dot m_{w} = \dot m_{ref }\cdot \frac{h_{ref,in}-h_{ref,out}}{h_{w,out}-h_{w,in}}$

Given that $h_{ref,in} = 808.34\,\frac{kJ}{kg}$ , $h_{ref, out} = 88.82\,\frac{kJ}{kg}$ , $h_{w,out} = 104.83\,\frac{kJ}{kg}$ and $h_{w,in} = 62.98\,\frac{kJ}{kg}$ , the mass flow of the cooling water is:

$\dot m_{w} = \left(7.2\,\frac{kg}{min} \right)\cdot \left(\frac{808.34\,\frac{kJ}{kg}-88.82\,\frac{kJ}{kg} }{104.83\,\frac{kJ}{kg}-62.98\,\frac{kJ}{kg} } \right)$

$\dot m_{w} = 123.788\,\frac{kg}{min}$

The mass flow rate of cooling water required to cool the refrigerant is $123.788\,\frac{kg}{min}$ .

4 0

3 years ago

zener shunt regulator employs a 9.1-V zener diode for which VZ = 9.1 V at IZ = 9 mA, with rz = 40 and IZK= 0.5 mA. The available

gulaghasi [49]

Answer:

$V_z=9.1v$

$V_{zo}=8.74V$

$I=10mA$

$R=589 ohms$

Explanation:

From the question we are told that:

Zener diode Voltage $V_z=9.1-V$

Zener diode Current $I_z=9 .A$

Note

$rz = 40\\\\IZK= 0.5 mA$

Supply Voltage $V_s=15$

Reduction Percentage $P_r= 50 \%$

Generally the equation for Kirchhoff's Voltage Law is mathematically given by

$V_z=V_{zo}+I_zr_z$

$9.1=V_{z0}+9*10^{-3}(40)$

$V_{zo}=8.74V$

Therefore

$At I_z-10mA$

$V_z=V_{z0}+I_zr_z$

$V_z=8.74+(10*10^{-3}) (40)$

$V_z=9.1v$

Generally the equation for Kirchhoff's Current Law is mathematically given by

$-I+I_z+I_l=0$

$I=10mA+\frac{V_z}{R_l}$

$I=10mA+\frac{9.1}{0}$

$I=10mA$

Therefore

$R=\frac{15V-V_z}{I}$

$R=\frac{15-9.1}{10*10^{-3}}$

$R=589 ohms$

5 0

3 years ago

The acceleration due to gravity on the surface of the moon is 1.62m/s^2. The moon's radius is Rm+1738km. A) What is the weight i

Anastaziya [24]

Answer:

weight is 12.6 N

force is 4.05 N

Explanation:

given data

acceleration = 1.62 m/s²

radius = 1738 km

mass = 10 kg

distance = 1738 km

to find out

weight and force

solution

we apply here weight formula that is

weight = mass × acceleration ...................1

put here value

weight = 10 × 1.26

weight = 12.6 N

and

force = mass × An

force = 10 × 1.62 (1738/ 1738+1738)² = 4.05 N

so force is 4.05 N

4 0

3 years ago

(a) In your own words, explain how donor impurities in semiconductors give rise to free electrons in numbers in excess of those

Kazeer [188]

Answer:

A. N type impurities

B. P type impurities

Explanation:

A. The impurities contribute free electrons and changing the conducting property of the semi conductor. When a pentavalent impurities in a semi conductor( impurities with five valence electron) , the impurity atom replace some of the semi conductor atoms in the crystal structure where 4 of the valence electron would be involved in bonding of 4 neighbouring semiconductor while leaving the fifth electron to be free(negative charge carrier) which is available for detachment.

B. When a trivalence impurity is added to semiconductor, instead of excess electron, there will be excess hole created by crystals. Reason for this attribute is the trivalence atom will replace some tetra valence semiconductor atom, when three valence electrons of the 3 valence electrons of the trivalent impurity atom make bond with three neighbouring semiconductor which gives rise to lack of electron in the bond of the fourth neighbouring semiconductor which contribute a whole to the crystalline since trivalent impurity contribute excess holes to the crystal of semi conductor, this holes can accept electrons.

8 0

3 years ago