PHYSICS HIGH SCHOOL

A container holding 1.2 kg of water at 20.0 °C is placed in a freezer that is kept at –20.0 °C. The water freezes and comes into thermal equilibrium with the interior of the freezer. a) How much heat is extracted from the water in thisprocess?
b) What is the minimum amount of electrical energy required bythe refrigerator to carry out this process if it operates betweenreservoirs at temperatures of 20.0 °C and -20.0 °C?

Answers

Answer 1

Answer:

Answer:

(a) $Q=556464\ J$

(b) 556464 joule

Explanation:

Given:

mass of water, $m_w=1.2\ kg$

initial temperature of water, $T_i=20^(\circ)C$

final temperature of frozen water, $T_f=-20{}^(\circ)C$

The conversion of water of 20.0 °C to the ice of –20.0 °C will comprise of three steps:

cooling of water to 0 °C $Q_w$
formation of ice at 0 °C from the water of 0 °C $Q_L$
further cooling of ice of 0 °C to -20 °C $Q_i$

We have,

Latent heat of fusion of ice, $L=3.4* 10^5\ J.kg^(-1)$

specific heat of water, $c_w=4186\ J.kg^(-1).^(\circ)C^(-1)$

specific heat of ice, $c_i=2000\ J.kg^(-1).^(\circ)C^(-1)$

(a)

Now, total heat lost in the process:

$Q=Q_w+Q_L+Q_i$

$Q=m_w(c_w. \Delta T_w+L+c_i.\Delta T_i)$

where:

$\Delta T_i\ \&\ \Delta T_w$ = change in temperature of ice and water respectively.

$\Rightarrow Q=1.2(4186* 20+3.4* 10^5+2000* 20)$

$Q=556464\ J$ is the total heat extracted during the process.

(b)

So, 556464 joule is the minimum electrical energy (by the law of energy conservation under no loss condition) required by refrigerator to carry out this process if it operates between the reservoirs at temperatures of 20.0 °C and -20.0 °C, because for a refrigerator to work in a continuous cycle it is impossible to transfer heat from a low temperature reservoir to a high temperature reservoir without consuming energy in the form of work. Here 556464 joule is the heat of the system to be eliminated.

Answer 2

Answer:

Final answer:

The amount of heat extracted from the water involves the sum of heat lost as it cools and then freezes. The minimum energy needed by the refrigerator to do this is given by the formula for Carnot efficiency.

Explanation:

To answer these questions, we'll need to understand some fundamental principles of thermodynamics.

a) The heat Q taken from the water will be the sum of the heat released during cooling of the water until 0.0°C, and the heat released during freezing at 0.0°C. The heat loss as the water cools can be calculated using Q = mcΔt where m=mass of water, c=specific heat of water, and Δt=change in temperature. The heat loss as water freezes can be calculated using Q = mlf where lf is the latent heat of fusion. Adding these two quantities gives the total heat extracted.

b) The minimum energy needed by the refrigerator, W, is given by the Carnot efficiency formula, W = Q*(T_hot - T_cold)/T_hot, where T is in Kelvin. This would tell you how much energy the refrigerator needs to remove the heat from the water and cool it down to the freezer temperature.

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Answers

Answer:

4 times

Explanation:

Since the equation for the illumination of an object, i.e. the brightness of the light, is inversely proportional to the square of the distance from the light source, the form of the function is:

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a 15kg child is riding a merry go round at 3rpm. what centripetal force must she exert if she is 8m from the center

Answers

This is another application of Newton's second law of motion

   Force = (mass) x (acceleration).

The quantities are a little more complicated in circular motion than
they are in plain old straight-line motion. In circular motion, the 'force'
is the centripetal force on the object, always pointing toward the center
of the circle. And the 'acceleration' is the centripetal acceleration, also
pointing toward the center of the circle, and equal to

      (speed)² / (radius).

The only thing we really need to find is the centripetal acceleration, and
then we'll have everything needed to plug into the formula and calculate
the centripetal force.

   Acceleration =    (speed)² / (radius).

   Speed = (distance) / (time) =

   (3 circumferences) / (minute) =

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(6 pi x 8 meters) / (60 sec) = 0.8 pi m/s .

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I would not say that she "exerts this centripetal force". The fact of
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exert on her, pointing toward the center, in order to keep her revolving
around the center at that speed. It could be the friction between her
shoes and the platform, if she's standing on the merry-go-round.
It could be a rope tied between her ankle and something at the center
of the rotating platform. It could be the safety belt on the horse that
she's riding. Whatever it is, something has to constantly pull her toward
the center of the platform, with a force of 11.84 newtons, otherwise her
15kg body will not travel in that circular path.

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Answers

We need to consider no change in the temperature of gas (isothermal transformation)

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Answers

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What is unit vector?

Physical quantities that exhibit both magnitude and direction are referred to as vector quantities. As an illustration, consider displacement, force, torque, momentum, acceleration, and velocity.

Typically, an arrow is used on top of a vector quantity to depict the vector value of the velocity and to clarify that the quantity has both magnitude and direction.

A quantity with both magnitude and direction is referred to as a vector. A unit vector is one with a magnitude of 1. It also goes by the name Direction Vector.

Given vector is :

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Hence, component of A vector along B vector is =

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So, the required component of vector is 7√2/2 unit.

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Answers

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