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2 years ago

12

Which of the following is the correct definition of conduction? A. the transfer of heat by currents within a liquid or gas B. th

e transmission of heat across matter C. the transmission of heat across empty space D. the electromagnetic radiation from the surface of an object which is due to the object's temperature

2 answers:

dolphi86 [110]2 years ago

6 0

I believe it's B. the transmission of heat across matter

salantis [7]2 years ago

6 0

B. the transmission of heat across matter

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A woman is straining to lift a large crate, without success because it is too heavy. We denote the forces on the crate as follow

Ymorist [56]

Answer:

Explanation:

Given

Force P is acting upward

C is vertical contact Force

W is the weight of the crate

As P is unable to move the Block therefore Normal reaction keeps on acting on block

thus we can say that

P-W+C=0

P=W-C

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2 years ago

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You may have noticed runaway truck lanes while driving in the mountains. These gravel-filled lanes are designed to stop trucks t

kati45 [8]

Answer:

The coefficient of kinetic friction $\mu_k = 0.724$

Explanation:

From the question we are told that

The length of the lane is $l = 36.0 \ m$

The speed of the truck is $v = 22.6\ m/s$

Generally from the work-energy theorem we have that

$\Delta KE = N * \mu_k * l$

Here N is the normal force acting on the truck which is mathematically represented as

$\Delta KE$ is the change in kinetic energy which is mathematically represented as

$\Delta KE = \frac{1}{2} * m * v^2$

=> $\Delta KE = 0.5 * m * 22.6^2$

=> $\Delta KE = 255.38m$

$255.38m = m * 9.8 * \mu_k * 36.0$

=> $255.38 = 352.8 * \mu_k$

=> $\mu_k = 0.724$

6 0

2 years ago

The magnetic field around the head has been measured to be approximately 3.00×10−8 gauss . Although the currents that cause this

konstantin123 [22]

Answer:

$3.81972\times 10^{-7}\ A$

Explanation:

B = Magnetic field = $3\times 10^{-8}\ G$

d = Diameter of loop = 16 cm

r = Radius = $\frac{d}{2}=\frac{16}{2}=8\ cm$

i = Current

$\mu_0$ = Vacuum permeability = $4\pi \times 10^{-7}\ H/m$

The magnetic field of a loop is given by

$B=\frac{\mu_0i}{2r}\\\Rightarrow i=\frac{B2r}{\mu_0}\\\Rightarrow i=\frac{3\times 10^{-8}\times 10^{-4}\times 2\times 0.08}{4\pi\times 10^{-7}}\\\Rightarrow i=3.81972\times 10^{-7}\ A$

The current needed to produce such a field at the center of the loop is $3.81972\times 10^{-7}\ A$

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2 years ago

Students use a stretched elastic band to launch carts of known mass horizontally on a track. The elastic bands exert a force F,

rodikova [14]

Answer:

the correct answer is E

A graph of the cart's maximum speed squared as a function of x^3

Explanation:

For this exercise let's use Newton's second law

F = m a

force has the form

F = k x²

and acceleration is related to velocity

a = dv / dt

Let's use the chain rule or L'Hospital

a = dv /dx dx/dt

a = dv /dx v

let's substitute

k x² = m v dv / dx

k /m x² dx = v dv

we integrate

k /m x³ /3 = v² / 2

v² = (2k /3m) x³

This is the expression for the variation of the speed as a function of the position, to make a linear graph realism the changes of variable

y = v²

x´ = x³

y = (2k/3m) x´

if we graph y vs x 'we have a linear graph whose slope is

m = 2k / 3m

By reviewing the different answers, the correct answer is E

4 0

2 years ago

A hot (70°C) lump of metal has a mass of 250 g and a specific heat of 0.25 cal/g⋅°C. John drops the metal into a 500-g calorimet

Gnom [1K]

Answer:

d. 37 °C

Explanation:

$m_{m}$ = mass of lump of metal = 250 g

$c_{m}$ = specific heat of lump of metal = 0.25 cal/g°C

$T_{mi}$ = Initial temperature of lump of metal = 70 °C

$m_{w}$ = mass of water = 75 g

$c_{w}$ = specific heat of water = 1 cal/g°C

$T_{wi}$ = Initial temperature of water = 20 °C

$m_{c}$ = mass of calorimeter = 500 g

$c_{c}$ = specific heat of calorimeter = 0.10 cal/g°C

$T_{ci}$ = Initial temperature of calorimeter = 20 °C

$T_{f}$ = Final equilibrium temperature

Using conservation of heat

Heat lost by lump of metal = heat gained by water + heat gained by calorimeter

$m_{m} c_{m} (T_{mi} - T_{f}) = m_{w} c_{w} (T_{f} - T_{wi}) + m_{c} c_{c} (T_{f} - T_{ci}) \\(250) (0.25) (70 - T_{f} ) = (75) (1) (T_{f} - 20) + (500) (0.10) (T_{f} - 20)\\T_{f} = 37 C$

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2 years ago