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3 years ago

What heat transfer occurs when warm air rises

1 answer:

3 0

Convection. When a fluid such as air or water touches a hot object, it can heat up and then move in bulk as a fluid, thereby carrying the heat quickly to new locations. Hot air rising is a common example of heat convection.

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A man walks along a straight path at a speed of 4 ft/s. A searchlight is located on the ground 6 ft from the path and is kept fo

BARSIC [14]

We are given that,

$\frac{dx}{dt} = 4ft/s$

We need to find $\frac{d\theta}{dt}$ when $x=8ft$

The equation that relates x and $\theta$ can be written as,

$\frac{x}{6} tan\theta$

$x = 6tan\theta$

Differentiating each side with respect to t, we get,

$\frac{dx}{dt} = \frac{dx}{d\theta} \cdot \frac{d\theta}{dt}$

$\frac{dx}{dt} = (6sec^2\theta)\cdot \frac{d\theta}{dt}$

$\frac{d\theta}{dt} = \frac{1}{6sec^2\theta} \cdot \frac{dx}{dt}$

Replacing the value of the velocity

$\frac{d\theta}{dt} = \frac{1}{6} cos^2\theta (4)^2$

$\frac{d\theta}{dt} = \frac{8}{3} cos^2\theta$

The value of $cos \theta$ could be found if we know the length of the beam. With this value the equation can be approximated to the relationship between the sides of the triangle that is being formed in order to obtain the numerical value. If this relation is known for the value of x = 6ft, the mathematical relation is obtained. I will add a numerical example (although the answer would end in the previous point) If the length of the beam was 10, then we would have to

$cos\theta = \frac{6}{10}$

$\frac{d\theta}{dt} = \frac{8}{3} (\frac{6}{10})^2$

$\frac{d\theta}{dt} = \frac{24}{25}$

Search light is rotating at a rate of 0.96rad/s

4 0

3 years ago

What force must be applied to move a 251 kg rock on a pavement like surface

Alchen [17]

If the rock is just sitting there and you want to SLIDE it, then you have to push it with a force of at least

(251 kg) x (9.8 m/s²) x (μ) =

(2,459 Newtons) x (the coefficient of static friction on that surface)

4 0

3 years ago

Westinghouse and edison fought what was known as the war of the currents. Eventually, westinghouse triumped using Alternating cu

Pachacha [2.7K]

This is because AC is easier to transform from a higher voltage to another, lower voltage, using transformers. High voltage means less <span>resistive losses in the power lines during transmission. This is why power is transmitted at many hundreds of thousands of volts and is only transformed into 110V or 220V near the consumers. </span>

3 0

4 years ago

Read 2 more answers

A mass of 2000 kg is raised 5.0 m in 10 seconds what is the potential energy of the mass at this height?

kvv77 [185]

Answer:

A. 98,000 J

Explanation:

The gravitational potential energy of an object is given by

U = mgh

where

m is the mass of the object

g is the gravitational acceleration

h is the heigth above the ground

In this problem,

m = 2000 kg

g = 9.8 m/s^2

h = 5.0 m

Substituting into the equation, we find

$U=(2000 kg)(9.8 m/s^2)(5.0 m)=98,000 J$

8 0

4 years ago

1) Find the voltage on a circuit with a resistance of 12.5 Ω if it has a current of 2.35 A.

KengaRu [80]

1. The voltage on the circuit with a resistance of 12.5 Ω and current of 2.35 A is 29.4 V.

2.The resistance in the circuit is found to be 1.45 Ω.

3. The equivalent resistance of the resistors connected in series is 24 Ω.

4. The equivalent resistance of the resistors connected in parallel is 2.18Ω.

5. The power generated is 552.5 W.

6. The frequency of the green light is 0.56×10¹⁵ Hz.

Explanation:

1) This problem can be solved using Ohm's law. Here the resistance (R) of the circuit is given to be 12.5 Ω and the current (I) is stated to be 2.35 A. So the ohm's law states that in a closed circuit, the voltage will be directly proportional to the current flowing in the circuit and the resistance will act as the proportionality constant.

$V = I * R = 2.35*12.5 = 29.4 V$

So, the voltage on the circuit with a resistance of 12.5 Ω and current of 2.35 A is 29.4 V.

2) Using the same Ohms' law, now we have to determine the resistance. So in this case, the voltage is given as 9 V and the current is said to be 6.2 A, then resistance can be determined as the ratio of voltage to current.

$R = \frac{V}{I} =\frac{9}{6.2} =1.45 Ohms$

So, the resistance in the circuit is found to be 1.45 Ω.

3) Here, the resistances of three resistors are given as 4 Ω, 8 Ω and 12 Ω. And it is stated that the resistances are connected or wired in series. Then the equivalent resistance will be obtained by the sum of resistances of three resistors, as the current flow will be constant in all the three resistors.

$R_{s} = R_{1} + R_{2} + R_{3} \\ \\R_{s} = 4+8+12 = 24 ohms$

Thus, the equivalent resistance of the resistors connected in series is 24 Ω.

4) Now, if the resistors are connected in parallel, then the equivalent resistance will be ratio of product of resistances to the sum of the resistances.

$\frac{1}{R_{p} }= \frac{1}{R_{1} } + \frac{1}{R_{2} } +\frac{1}{R_{3} }\\\\\frac{1}{R_{p} }=\frac{1}{4}+ \frac{1}{8} +\frac{1}{12} = \frac{6+3+2}{24} =\frac{11}{24} \\\\R_{p} = \frac{24}{11 } =2.18 Ohm$

Thus, the equivalent resistance of the resistors connected in parallel is 2.18Ω.

5) Power generated by the person can be obtained by the ratio of work done by the person to the time in which the work is done. So the work done can be obtained by the product of force with displacement.

As here the weight lifted by the person will act as dominant force on the person. So the force is considered as F = 956 N and the displacement is d = 2.41 m, then

$Work done = Force * displacement = 956*2.41 =2303.96 J$

So, the work done is obtained as 2303.96 J and the time is given as 4.17 s, then

$Power = \frac{Work done}{Time} =\frac{2303.96}{4.17} =552.5 W$

So, the power generated is 552.5 W.

6) In this, the wavelength of green light is given as 5.34 × 10⁻⁷ m. It is known that the wavelength is inversely proportional to the frequency.

$Wavelength = \frac{Speed of light}{Frequency}$

As, speed of light is known as 3×10⁸ m/s, the frequency will be determined as the ratio of speed of light to wavelength.

$Frequency = \frac{Speed of light}{Wavelength} =\frac{3*10^{8} }{5.34*10^{-7} } \\\\Frequency =0.56*10^{15} Hz$

Thus, the frequency of the green light is 0.56×10¹⁵ Hz.

8 0

4 years ago