2. A ball is dropped from rest. The acceleration due to gravity is 10m/s? and the time it

When an aluminum bar is connected between a hot reservoir at 720 K and a cold reservoir at 358 K, 3.00 kJ of energy is transferr

disa [49]

Answer:

a. -4.166 J/K

b. 8.37 J/K

c. 4.21 J/K

d. entropy always increases.

Explanation:

Given :

Temperature at hot reservoir , $T_h$ = 720 K

Temperature at cold reservoir , $T_c$ = 358 K

Transfer of heat, dQ = 3.00 kJ = 3000 J

(a). In the hot reservoir, the change of entropy is given by:

$dS_h= -\frac{dQ}{t_h}$ (the negative sign shows the loss of heat)

$dS_h= -\frac{3000}{720}$

= -4.166 J/K

(b) In the cold reservoir, the change of entropy is given by:

$dS_c= \frac{dQ}{t_c}$

$dS_c= \frac{3000}{358}$

= 8.37 J/K

(c). The entropy change in the universe is given by:

$dS=dS_h+dS_c$

= -4.16+8.37

= 4.21 J/K

(d). According to the concept of entropy, the entropy of the universe is always increasing and never decreasing for an irreversible process. If the entropy of universe decreases, it violates the laws of thermodynamics. Hence, in part (c), the result have to be positive.

5 0

3 years ago

If an object accelerating at −1.5m/s^2 takes 1.2s to reach 5.0m/s, what was its initial speed?

USPshnik [31]

-1.5 m/s^2 x 1.2 seconds = -1.8 m/s

It is a negative value which means the object slowed down. The object would have originally been going that amount more.

5.0 + 1.8 = 6.8 m/s

answer: 6.8 m/s

3 0

2 years ago

Traveling waves propagate with a fixed speed usually denoted as v (but sometimes c). The waves are called __________ if their wa

Snezhnost [94]

Answer:

Periodic.

Explanation:

Electromagnetic waves is a propagating medium used in all communications device to transmit data (messages) from the device of the sender to the device of the receiver.

Generally, the most commonly used electromagnetic wave technology in telecommunications is radio waves.

Radio waves can be defined as an electromagnetic wave that has its frequency ranging from 30 GHz to 300 GHz and its wavelength between 1mm and 3000m. Therefore, radio waves are a series of repetitive valleys and peaks that are typically characterized of having the longest wavelength in the electromagnetic spectrum.

Basically, as a result of radio waves having long wavelengths, they are mainly used in long-distance communications such as the carriage and transmission of data.

Generally, a fixed speed is used for the propagation of traveling waves and this speed is usually denoted with the variable "v" or sometimes "c."

Furthermore, if the waveform of a traveling wave is repeated every time at specific intervals T, it is referred to as periodic wave.

Mathematically, the period of a traveling wave is given by the formula;

$Period = \frac {1}{T}$

Where;

T is the time measured in seconds.

5 0

3 years ago

A solar cell generates a potential difference of 0.25 V when a 550 Ω resistor is connected across it, and a potential difference

Andre45 [30]

a) $400 \Omega$

b) 0.43 V

c) 0.44 %

Explanation:

a)

For a battery with internal resistance, the relationship between emf of the battery and the terminal voltage (the voltage provided) is

$V=E-Ir$ (1)

where

V is the terminal voltage

E is the emf of the battery

I is the current

r is the internal resistance

In this problem, we have two situations:

1) when $R_1=550 \Omega$ , $V_1=0.25 V$

Using Ohm's Law, the current is:

$I_1=\frac{V_1}{R_1}=\frac{0.25}{550}=4.5\cdot 10^{-4} A$

2) when $R_2=1000 \Omega$ , $V_2=0.31 V$

Using Ohm's Law, the current is:

$I_2=\frac{V_2}{R_2}=\frac{0.31}{1000}=3.1\cdot 10^{-4} A$

Now we can rewrite eq.(1) in two forms:

$V_1 = E-I_1 r$

$V_2=E-I_2 r$

And we can solve this system of equations to find r, the internal resistance. We do it by substracting eq.(2) from eq(1), we find:

$V_1-V_2=r(I_2-I_1)\\r=\frac{V_1-V_2}{I_2-I_1}=\frac{0.25-0.31}{3.1\cdot 10^{-4}-4.5\cdot 10^{-4}}=400 \Omega$

b)

To find the electromotive force (emf) of the solar cell, we simply use the equation used in part a)

$V=E-Ir$

where

V is the terminal voltage

E is the emf of the battery

I is the current

r is the internal resistance

Using the first set of data,

$V=0.25 V$ is the voltage

$I=4.5\cdot 10^{-4}A$ is the current

$r=400\Omega$ is the internal resistance

Solving for E,

$E=V+Ir=0.25+(4.5\cdot 10^{-4})(400)=0.43 V$

c)

In this part, we are told that the area of the cell is

$A=4.0 cm^2$

While the intensity of incoming radiation (the energy received per unit area) is

$Int.=5.5 mW/cm^2$

This means that the power of the incoming radiation is:

$P=Int.\cdot A=(5.5)(4.0)=22 mW = 0.022 W$

This is the power in input to the resistor.

The power in output to the resistor can be found by using

$P'=I^2R$

where:

$R=1000 \Omega$ is the resistance of the resistor

$I=3.1\cdot 10^{-4} A$ is the current on the resistor (found in part A)

Susbtituting,

$P'=(3.1\cdot 10^{-4})^2(1000)=9.61\cdot 10^{-5} W$

Therefore, the efficiency of the cell in converting light energy to thermal energy is:

$\epsilon = \frac{P'}{P}\cdot 100 = \frac{9.6\cdot 10^{-5}}{0.022}=0.0044\cdot 100 = 0.44\%$

7 0

3 years ago

Match the chemical formula to the correct name.

11Alexandr11 [23.1K]

Co carbon monoxide
sorry friend i don't know other ones

3 0

3 years ago