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Dmitry_Shevchenko [17]
3 years ago
10

(a) What is the cost of heating a hot tub containing 1440 kg of water from 10.0°C to 40.0°C, assuming 75.0% efficiency to take h

eat loss to surroundings into account? The cost of electricity is 9.00¢/(kW · h) and the specific heat for water is 4184 J/(kg · °C). $ 67 Incorrect: Your answer is incorrect. How much heat is needed to raise the temperature of m kg of a substance? How many joules are in 1 kWh? (b) What current was used by the 220 V AC electric heater, if this took 3.45 h? 88.2 Correct: Your answer is correct. A
Physics
1 answer:
BaLLatris [955]3 years ago
7 0

Answer:

a) E = 6.024\,USD, For m kilograms, it is 4184m J., 3600000 joules, b) i = 88.200\,A

Explanation:

a) The amount of heat needed to warm water is given by the following expression:

Q_{needed} = m_{w}\cdot c_{w}\cdot (T_{f}-T_{i})

Where:

m_{w} - Mass of water, measured in kilograms.

c_{w} - Specific heat of water, measured in \frac{J}{kg\cdot ^{\circ}C}.

T_{f}, T_{i} - Initial and final temperatures, measured in ^{\circ}C.

Then,

Q_{needed} = (1440\,kg)\cdot \left(4184\,\frac{J}{kg\cdot ^{\circ}C} \right)\cdot (40^{\circ}C - 10^{\circ}C)

Q_{needed} = 180748800\,J

The energy needed in kilowatt-hours is:

Q_{needed} = 180748800\,J\times \left(\frac{1}{3600000}\,\frac{kWh}{J} \right)

Q_{needed} = 50.208\,kWh

The electric energy required to heat up the water is:

E = \frac{50.208\,kWh}{0.75}

E = 66.944\,kWh

Lastly, the cost of heating a hot tub is: (USD - US dollars)

E = (66.944\,kWh)\cdot \left(0.09\,\frac{USD}{kWh} \right)

E = 6.024\,USD

The heat needed to raise the temperature a degree of a kilogram of water is 4184 J. For m kilograms, it is 4184m J. Besides, a kilowatt-hour is equal to 3600000 joules.

b) The current required for the electric heater is:

i = \frac{Q_{needed}}{\eta \cdot \Delta V \cdot \Delta t}

i = \frac{180748800\,J}{0.75\cdot (220\,V)\cdot (3.45\,h)\cdot \left(3600\,\frac{s}{h} \right)}

i = 88.200\,A

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Answer:

60

Explanation:

Translation -

A book weighing 12 N is balanced on a table. Knowing that the static friction coefficient is 0.5, how much is the friction force worth?

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3 years ago
A ceiling fan has three blades. The moment of inertia of a blade is 0.2kgm^2. The net torque exerted on fan blades is 8Nm. Find
olchik [2.2K]

Answer:

(A) the angular acceleration of the blades is 13.33 m/s.

Explanation:

Given;

moment of inertia of a blade, I = 0.2 kgm²

net torque exerted on fan blades, ∑τ =  8Nm

Torque is given as product of moment of inertia and angular acceleration;

τ = Iα

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α is the angular acceleration

Since there are three blades of the ceiling fan, the net torque is given as;

∑τ = (3I)α

∑τ = 3Iα

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α = (8) / (3 x 0.2)

α = 13.33 m/s

Therefore, the angular acceleration of the blades is 13.33 m/s.

8 0
2 years ago
Which equation is used to determine the density of a substance?
Mademuasel [1]
The answer is D=M/V hope it helps!!
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3 years ago
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When is the magnitude of the acceleration of a mass on a spring at its maximum value?
Andreas93 [3]

Answer:

A. when the mass has a speed of zero

Explanation:

In mass-spring system, the velocity and the acceleration are in anti-phase, which means that when one of the two quantities is maximum, the other one is zero, and vice-versa.

In fact:

- When the displacement of the spring is zero (x=0), the velocity is maximum, due to conservation of energy. In fact, as the displacement is zero, the elastic potential energy of the system (given by \frac{1}{2}kx^2) is zero, therefore the kinetic energy (given by \frac{1}{2}mv^2) must be maximum, and so the velocity (v) is also maximum. On the cotnrary, acceleration (a) is directly proportional to the restoring force of the spring, given by

F=-kx

so we see that when x=0, then the force is zero: F=0, and so the acceleration is zero as well.

- When the displacement of the spring is maximum, the velocity is zero, due to conservation of energy. In fact, as the displacement is maximum, the elastic potential energy of the system (given by \frac{1}{2}kx^2) is maximum, therefore the kinetic energy (given by \frac{1}{2}mv^2) must be zero, and so the velocity (v) is also zero. On the cotnrary, since acceleration (a) is directly proportional to the restoring force of the spring, given by

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so we see that when x=maximum, then the force is maximum, and so the acceleration is maximum as well.

Based on this, the correct answer is

A. when the mass has a speed of zero


5 0
2 years ago
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Gulls are often observed dropping clams and other shellfish from a height to the rocks below, as a means of opening the shells.
kumpel [21]

Answer:

v = 17.71 m / s

Explanation:

We can work this exercise with the kinematics equations. In general the body is released so that its initial velocity is zero, the acceleration of the acceleration of gravity

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                v² = 0 - 2g (y -y₀)

when it hits the stone the height is zero and part of the height of the seagull I

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let's calculate

              v =√ (2 9.8 16)

              v = 17.71 m / s

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