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diamong [38]
3 years ago
12

A newly proposed device for generating electricity from the sun is a heat engine in which the hot reservoir is created by focusi

ng sunlight on a small spot on one side of the engine. The cold reservoir is ambient air at 20°C. The designer claims that the efficiency will be 50%.
What minimum hot-reservoir temperature, in degrees C, would be required to produce this efficiency?
Physics
1 answer:
Art [367]3 years ago
5 0

Answer:  

The minimum temperature of hot reservoir is 586K or 313°C

Explanation:

The<em> Carnot cycle</em> is defined as ideal reversible process thermodynamic process which has four successive step. During the expansion and compression of  the substance it can done upto desired point and then reversed up.

Here the energy is used from the hot reservoir to do work and deposited into the cold reservoir. As is it reversible the efficiency of the carnot cycle is the theoretical maximum of the heat engine.

<em>The efficiency of carnot cycle is</em>

η = 1 - \frac{Tc}{Th}    eq 1

Where Tc is the temperature of cold reservoir = 20° = 20°+273K = 293K

           Th is the temperature of hot reservoir.

            η  is the efficency 50% = 0.5

The minimum temperature of the reservoir is related to the maximum efficiency,

Substituting values in eqn 1

0.05 = 1-\frac{293}{Th}

Th = \frac{293}{1 - 0.5} =586 K

<em>The minimum temperature of hot reservoir is 586K.</em>

ie 586K-273 = 313°C

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4 0
4 years ago
What are the postulates of STR?
Dafna11 [192]

Answer:

The laws of physics take the same form in all inertial frames of reference. As measured in any inertial frame of reference, light is always propagated in empty space with a definite velocity c that is independent of the state of motion of the emitting body.

6 0
4 years ago
How many milliliters of water at 25.0°C with a density of 0.997 g/mL must be mixed with 162 mL of coffee at 94.6°C so that the r
Andre45 [30]

Answer:

The volume of water is 139 mL.

Explanation:

Due to the Law of conservation of energy, the heat lost by coffee is equal to the heat gained by the water, that is, the sum of heats is equal to zero.

Q_{coffee} + Q_{water} = 0\\Q_{coffee} = - Q_{water}

The heat (Q) can be calculated using the following expression:

Q=c \times m \times \Delta T

where,

c is the specific heat of each substance

m is the mass of each substance

ΔT is the difference in temperature for each substance

The mass of coffee is:

162mL.\frac{0.997g}{mL} = 162g

Then,

Q_{coffee} = - Q_{water}\\c_{c} \times m_{c} \times \Delta T_{c} = -c_{w} \times m_{w} \times \Delta T_{w}\\m_{c} \times \Delta T_{c} = -m_{w} \times \Delta T_{w}\\m_{w} = \frac{m_{c} \times \Delta T_{c}}{-\Delta T_{w}} \\m_{w}=\frac{162g \times (62.5 \°C - 94.6 \°C ) }{-(62.5 \°C - 25.0 \°C)} \\m_{w} = 139 g

The volume of water is:

139g.\frac{1mL}{0.997g} =139mL

7 0
4 years ago
The acceleration vector of a particle in projectile motion ________.
Alex73 [517]

Answer:

Points downward, and its magnitude is 9.8 m/s^2

Explanation:

The motion of a projectile consists of two independent motions:

- A uniform horizontal motion, with constant velocity and zero acceleration. In fact, there are no forces acting on the projectile along the horizontal direction (if we neglect air resistance), so the acceleration along this direction is zero.

- A vertical motion, with constant acceleration g = 9.8 m/s^2 towards the ground (downward), due to the presence of gravity wich "pulls" the projectile downward.

The total acceleration of the projectile is given by the resultant of the horizontal and vertical components of the acceleration. But we said that the horizontal component is zero, therefore the total acceleration corresponds just to its vertical component, therefore it is a vector with magnitude 9.8 m/s^2 which points downward.

4 0
3 years ago
When a 100-N force acts horizontally on an 8.0-kg chair, the chair moves at a constant speed across the level floor. Which state
TiliK225 [7]

Answer:

The applied force is greater than the frictional force.

Explanation:

the chair moves at <u>a constant speed</u><u> </u><u>therefore</u><u>,</u><u> </u><u>the</u><u> </u><u>answer</u><u> </u><u>is</u><u> </u><u>not</u><u> </u><u>A</u><u> </u><u>or</u><u> </u><u>C</u><u>.</u>

if there is no friction then the chair <u>would accelerate and it would not be at a constant speed</u><u>.</u>

hence, the only possible answer is B.

7 0
3 years ago
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