Somebody please help me!! Timed test

Two parallel disks of diameter D 5 0.6 m separated by L 5 0.4 m are located directly on top of each other. Both disks are black

oksian1 [2.3K]

To solve this problem it is necessary to apply the concepts related to the Stefan-Boltzmann law which establishes that a black body emits thermal radiation with a total hemispheric emissive power (W / m²) proportional to the fourth power of its temperature.

Heat flow is obtained as follows:

$Q = FA\sigma\Delta T^4$

Where,

F =View Factor

A = Cross sectional Area

$\sigma =$ Stefan-Boltzmann constant

T= Temperature

Our values are given as

D = 0.6m

$L = 0.4m\\T_1 = 450K\\T_2 = 450K\\T_3 = 300K$

The view factor between two coaxial parallel disks would be

$\frac{L}{r_1} = \frac{0.4}{0.3}= 1.33$

$\frac{r_2}{L} = \frac{0.3}{0.4} = 0.75$

Then the view factor between base to top surface of the cylinder becomes $F_{12} = 0.26$ . From the summation rule

$F_{13} = 1-0.26$

$F_{13} = 0.74$

Then the net rate of radiation heat transfer from the disks to the environment is calculated as

$\dot{Q_3} = \dot{Q_{13}}+\dot{Q_{23}}$

$\dot{Q_3} = 2\dot{Q_{13}}$

$\dot{Q_3} = 2F_{13}A_1 \sigma (T_1^4-T_3^4)$

$\dot{Q_3} = 2(0.74)(\pi*0.3^2)(5.67*10^{-8})(450^4-300^4)$

$\dot{Q_3} = 780.76W$

Therefore the rate heat radiation is 780.76W

5 0

3 years ago

ANSWER ALL QUESTIONS AND GET 100 PONTS ALONG WITH BRAINLIEST

dmitriy555 [2]

Answer:

To not exceed the 5,000 characters, see each answer with its explanation below.

Explanation:

Question 1.

A feather and a rock dropped at the same time from the same height would land at the same time when dropped by an astronaut on the moon.

The shape and mass of the feather that falls vertically down, through the air, cause the resistance of the air, that opposes the gravitational attraction of the Earth, to be considerably large, compared to the case of the rock.

This not negligible resistance of the air causes a drag on the feather that makes it fall more slowly than the rock.

Only on the moon, the almost absence of atmosphere (air) would cause the feather not to be dragged and, therefore, its acceleration will be the same as that of the rock, and both will fall with the same speed and land at the same time (there is a video in the internet that shows this experiment of the astronaut on the moon).

Question 2.

When the soccer ball is kicked, the action and reaction forces do not cancel each other out because the forces act on two different objects.

The third law of Newton, also known as the law of action and reaction, states that whenever an object experience a force (action force) from a second object, the first object will exert a force of equal size and opposite in direction (reaction force) over the second object.

Hence, the action and reaction forces act over distinct objects. The ball feels the action force (the kick) and the foot feels the reaction force from the ball; the forces do not cancel each other because they act on two different objects.

Question 3

An object is in projectile motion if it is thrown with a horizontal push.

The projectile motion is the combination of two motions: vertical motion and horizonal motion.

The vertical motion is ruled by the acceleration of gravity and will depend on both the inital vertical velocity and the acceleration of gravity.

The horizontal motion is ruled by the horizontal velocity. According with the inertia law (first law of Newton), in the absence of a horizontal force, only if the object departs with a horizontal velocity it will move horizontally.

Hence, an object can only be in projectile motion if it is thrown with a horizontal push.

Question 4

Acceleration of an object

increases as the force on the object increases.

decreases as the mass of the object increases.

is in the same direction as the force on the object.

All answers listed. ← correct answer

According to second law of Newton

$\vec{F}=m\times \vec{a}$

This is force equals mass time acceleration.

The force is a vector and the acceleration is a vector, then since mass is a positive scalar magnitude, both force and acceleration have the same direction.

Also, it is clear from the definition of force that it is proportional to both, the mass and the acceleration, then if either mass or acceleration increases (while the other remains equal) the force will increase, and if either mass or acceleration decreases (while the other remains constant) the force will decrease.

Hence, all the options are correct.

Question 5

The bowling ball will have more momentum because it has more mass.

Momentum, P, is the product of the mass (m) and the velocity (v).

$\vec{P}=m\times \vec{v}$

It is clear that the mass of the bowling ball is greater than the mass of the golf ball.

Hence, since they are moving at the same velocity, the product of the mass of the bowling ball times the velocity is greater than the product of the golf mass times the same velocity.

Question 6

An orbit is formed when an object is falling around another object, rather than into it.

An example of an object falling around another object is a rock falling in the Earth. The gravitaional pull of the Earth causes that the rock accelerates and falls vertically downward.

An example of an object falling around another object is a satellite around the Earth.

The Earth is continually pulling the satellite with vertical force and the inertia (initial velocity) of the satellite is causing it to move horizontally.

The combination of the gravitational force and the inertia cause the satellite to follow a projectile motion. When the satellite is to the correct distance it will not reach into the Earth but will continually move around the Earth following a circular path named orbit.

Question 7

When the force of gravity is matched by the force of air resistance, an object can reach terminal velocity (two word answer).

When the force of gravity matches the force of air resistance, the net force on the falling object is zero.

Hence, as per the second Law of Newton, force equals the product of the mass and the acceleration, the acceleration is also zero.

Zero acceleration means constant velocity.

That constant velocity is a limit or maximum for the velocity that an object can reach when falling and is called terminal velocity.

3 0

3 years ago

A truck is traveling at 74.5 kilometers per hour away from you. The driver is blowing the horn which has a frequency of 415 Hz.

ArbitrLikvidat [17]

It would be a high pitched sound. Hope this helps.

8 0

3 years ago

Is using a heater to keep warm when it is cold conduction convection or radiation

Dmitry_Shevchenko [17]

Answer: convection

Explanation:

8 0

2 years ago

Three joules of work is needed to shift 10 C of charge from one place to another. The potential difference between the places is

dimaraw [331]

Answer:

The potential difference between the places is 0.3 V.

∴ 1st option i.e. 0.3V is the correct option.

Explanation:

Given

Work done W = 3J

Amount of Charge q = 10C

To determine

We need to determine the potential difference V between the places.

The potential difference between the two points can be determined using the formula

Potential Difference (V) = Work Done (W) / Amount of Charge (q)

or

$\:V\:=\:\frac{W}{q}$

substituting W = 3 and q = 10 in the formula

$V=\frac{3}{10}$

$V=0.3$ V

Therefore, the potential difference between the places is 0.3 V.

∴ 1st option i.e. 0.3V is the correct option.

4 0

3 years ago