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AVprozaik [17]
3 years ago
6

A 0.25-kg coffee mug is made from a material that has a specific heat capacity of 950 J/(kg · C°) and contains 0.30 kg of water.

The cup and water are at 25° C. To make a cup of coffee, a small electric heater is immersed in the water and brings it to a boil in two minutes. Assume that the cup and water always have the same temperature and determine the minimum power rating of this heater.
Physics
1 answer:
noname [10]3 years ago
5 0

Answer:

The minimum power neccesary is:

P=932,4 W

Explanation:

The water is bring to a boil so it goes from 25°C to 100°C, the temperature rise si:

dT=100°C-25°C=75°C

Considering that the cup is always at the same temperatura as the water the trasfered energy can be calculated as:

Q=(m_{mug}*C_{p-mug}+m_{water}*C_{p-water})*dT

We have that: m_{mug}=0,25kg, C_{p-mug}=950 J/(kg.°C), m_{water}=0,30kg, C_{p-water}=4180 J/(kg.°C) (considering it constant)

So:

Q=(0,25kg*950 J/(kg.°C)+0,30kg*4181 J/(kg.°C))*75°C

Q=1491,8J/°C*75°C=111885 J

Given that this energy was supplied in 2 minutes:

t=2 min=120 sec

The minimum power neccesary is:

P=\frac{Q}{t}=932,4 W

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alexandr1967 [171]

Answer:

(This will depend on the type of fuel, I will assume that the fuel is petrol)

First, let's find the expected energy consumption in the US for the next 10 years.

We know that in one year, a person consumes 3.5*10^11 joules.

There are 310,000,00 people on the US

Then the total consumption in one year is:

310,000,000*3.5*10^11 joules = 1.085*10^20 J

In 10 years the consumption is 10 times the consumption of a single year, then the expected energy consumption in the US for the next 10 years is:

10*1.085*10^20 J = 1.085*10^21 J

Now let's find the mass of fuel required.

We know that a liter of petrol has 31,536,000 joules of energy,

And a liter of petrol weights 0.75 kg

To find the number of liters of petrol that we need, we need to find the quotient between the expected energy consumption in the next 10 years and the energy of a single liter of petrol, this is:

N = (1.085*10^20 J)/(31,536,000 j) = 3.44*10^13

We will need  3.44*10^13 liters of petrol.

And the total mass of petrol will be:

M = 3.44*10^13*0.75 kg = 2.58*10^13 kg of fuel.

8 0
3 years ago
What is the final concentration of DD at equilibrium if the initial concentrations are [A][A]A_i = 1.00 MM and [B][B]B_i = 2.00
pentagon [3]

Answer:

A) Concentration of A left at equilibrium of we started the reaction with [A] = 2.00 M and [B] = 2.00 M is 0.55 M.

B) Final concentration of D at equilibrium if the initial concentrations are [A] = 1.00 M and [B] = 2.00 M is 0.90 M.

[D] = 0.90 M

Explanation:

With the first assumption that the volume of reacting mixture doesn't change throughout the reaction.

This allows us to use concentration in mol/L interchangeably with number of moles in stoichiometric calculations.

- The first attached image contains the correct question.

- The solution to part A is presented in the second attached image.

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zaharov [31]
I don’t know sorry then ya soo
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An offshore oil well is 2 kilometers off the coast. The refinery is 4 kilometers down the coast. Laying pipe in the ocean is twi
shusha [124]

Answer:

Rectangular path

Solution:

As per the question:

Length, a = 4 km

Height, h = 2 km

In order to minimize the cost let us denote the side of the square bottom be 'a'

Thus the area of the bottom of the square, A = a^{2}

Let the height of the bin be 'h'

Therefore the total area, A_{t} = 4ah

The cost is:

C = 2sh

Volume of the box, V = a^{2}h = 4^{2}\times 2 = 128            (1)

Total cost, C_{t} = 2a^{2} + 2ah            (2)

From eqn (1):

h = \frac{128}{a^{2}}

Using the above value in eqn (1):

C(a) = 2a^{2} + 2a\frac{128}{a^{2}} = 2a^{2} + \frac{256}{a}

C(a) = 2a^{2} + \frac{256}{a}

Differentiating the above eqn w.r.t 'a':

C'(a) = 4a - \frac{256}{a^{2}} = \frac{4a^{3} - 256}{a^{2}}

For the required solution equating the above eqn to zero:

\frac{4a^{3} - 256}{a^{2}} = 0

\frac{4a^{3} - 256}{a^{2}} = 0

a = 4

Also

h = \frac{128}{4^{2}} = 8

The path in order to minimize the cost must be a rectangle.

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murzikaleks [220]

Jennifer

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