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baherus [9]
3 years ago
15

A refrigerator is removing heat from a cold medium at 3∘C at a rate of 5400 kJ/h and rejecting the waste heat to a medium at 30∘

C. If the coefficient of performance of the refrigerator is 2, the power consumed by the refrigerator is
(a) 0.5 kW
(b) 0.75 kW
(c) 1.0 kW
(d) 1.5 kW
(e) 3.0 kW
Physics
1 answer:
ipn [44]3 years ago
3 0

Answer:(b) 0.75 kW

Explanation:

Given

temperature of cold region T_L=3^{\circ}C

Heat removal at the rate of Q_1=5400 kJ/h

temperature of hot region T_H=30^{\circ}C

COP of refrigerator =2

COP of a refrigerator is given by ratio of desired effect to the Power input

COP=\frac{Q_1}{Power}

2=\frac{5400}{P}

P=2700 kJ/h

P=0.75 kW

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At what speed does a falling hailstone travel? Does the speed depend on the distance that the hailstone falls?
Anton [14]

Answer:The speed if hailstone dependly largely on its size. A hailstone with a diameter of 0.39 inches,falls wit a speed of 20mph while a hailstone with 3.1 inches in diameter falls at a speed of 110mph.

No speed does not depend on the distance that the hailstone falls.

Explanation: There are other factors that affect the speed of the falling hailstone apart from its size.They are:

1. Friction between the air and the hailstone

2. Wind condition( windy or moist air)

3. The rate at which it melts falling.

7 0
3 years ago
Moving the probe 1 cm towards the non-grounded electrode changes the value the potential from about 0.90 V to about 1.2 V. Expla
svp [43]

Answer:

-30 N/C

Explanation:

Since the potential changes from 0.90 V to 1.2 V when I move the probe 1 cm closer to the non-grounded electrode, the electric field is the gradient between the two points is given by E = -ΔV/Δx where ΔV = change in electric potential and Δx = distance of potential change = 1 cm = 0.01 m

Now ΔV = final potential - initial potential = 1.2 V - 0.90 V = 0.30 V

Since E = -ΔV/Δx

substituting the values of the variables into the equation, we have

E = -ΔV/Δx

E = -0.30 V/0.01 m

E = -30 V/m

Since 1 V/m = 1 N/C.

E = -30 N/C

So, the average electric field is -30 N/C

6 0
3 years ago
A 1150 kg pile driver is used to drive a steel I-beam into the ground. The pile driver falls 7.69 m before contacting the beam,
Natasha_Volkova [10]

Answer:

the average force 11226 N  

Explanation:

Let's analyze the problem we are asked for the average force, during the crash, we can find this from the impulse-momentum equation, but this equation needs the speeds and times of the crash that we could look for by kinematics.

Let's start looking for the stack speeds, it has a free fall, from rest  (Vo=0)

             

           Vf² = Vo² - 2gY

            Vf² = 0 - 2 9.8 7.69 = 150.7

            Vf = 12.3 m / s

This is the speed that the battery likes when it touches the beam.  They also give us the distance it travels before stopping, let's calculate the time

         

            Vf = Vo - g t

             0 = Vo - g t

             t = Vo / g

             t = 12.3 / 9.8

             t = 1.26 s

This is the time to stop

Now let's use the equation that relates the impulse to the amount of movement

                 I = Δp

                F t = pf-po

The amount of final movement is zero because the system stops

                F = - po / t

                F = - mv / t

                F = - 1150 12.3 / 1.26

                F = -11226 N

This is the average force exerted by the stack on the vean

7 0
3 years ago
A migrating robin flies due north with a speed of 12 m/s relative to the air. The air moves due east with a speed of 6.3 m/s rel
Sonja [21]

consider east-west direction along X-axis  and north-south direction along Y-axis

V_{ra} = velocity of migrating robin relative to air = 12 j m/s

(where "j" is unit vector in Y-direction)

V_{ag} = velocity of air relative to ground = 6.3 i m/s

(where "i" is unit vector in X-direction)

V_{rg} = velocity of migrating robin relative to ground = ?

using the equation

V_{rg} = V_{ra} + V_{ag}

V_{rg} = 12 j + 6.3 i

V_{rg} = 6.3 i + 12 j

magnitude : sqrt((6.3)² + (12)²) = 13.6 m/s

direction : tan⁻¹(12/6.3) = 62.3 deg north of east

4 0
3 years ago
4 A magnet can exert a force of attraction or a force of repulsion on another magnet.
GenaCL600 [577]

Answer:

Push -repulsion

Pull - attraction

Explanation:

When two magnets are brought together, a push happens when a force of repulsion is experienced where the magnets move away from each other. This means their polarity is the same and this will cause the magnet to push away from each other.

When two magnets are brought together , a pull happens when a force of attraction is experienced where the magnets move close to each other. This means their polarity is different and thus causes the magnets to pull closer to each other.

7 0
3 years ago
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