3 years ago

What are the three points of the fire triangle

Physics

1 answer:

prisoha [69]3 years ago

5 0

1-fuel
2-heat
3-oxygen

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Compared with the Earth's atmosphere, the atmosphere of Venus is much _______, has a greater percentage of CO2, and has a ______

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1.A thicker stronger

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A transformer is used to light a lamp rated 40w, 240v from a 400v A.C supply. Calculate:

zubka84 [21]

Answer:1.81

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400÷220=1.81.

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3 years ago

A marble rolls with a speed of 15 m/s and has a momentum of 0.15 kg*m/s. What is its mass?<br>

prisoha [69]

Answer:

m = 0.01 kg

Explanation:

Given that,

Momentum of the marble, p = 0.15 kg-m/s

Speed of the marble, v = 15 m/s

We need to find its mass. We know that,

Momentum, p = mv

Where

m is the mass

$m=\dfrac{p}{v}\\\\m=\dfrac{0.15}{15}\\\\m=0.01\ kg$

So, the mass of the marble is equal to 0.01 kg.

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How much do you have to increase the vertical distance to double the impact speed of an object?

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3 years ago

A long copper rod of diameter 2.0 cm is initially at a uniform temperature of 100°C. It is now exposed to an air stream at 20°C

Lisa [10]

Answer:

t = 4.0 min

Explanation:

given data:

diameter of rod = 2 cm

T_1 = 100 degree celcius

Air stream temperature = 20 degree celcius

heat transfer coefficient = 200 W/m2. K

WE KNOW THAT

copper thermal conductivity = k = 401 W/m °C

copper specific heat Cp = 385 J/kg.°C

density of copper = 8933 kg/m3

charateristic length is given as Lc

$Lc = \frac{V}{A_s}$

$Lc = \frac{\frac{\pi D^2}{4} L}{\pi DL}$

$Lc = \frac{D}{4}$

$Lc = \frac{0.02}{6} = 0.005 m$

Biot number is given as $Bi = \frac{hLc}{k}$

$Bi = \frac{200*0.005}{401}$

Bi = 0.0025

As Bi is greater than 0.1 therefore lumped system analysis is applicable

so we have

$\frac{T(t) - T_∞}{Ti - T_∞} = e^{-bt}$ ............1

where b is given as

$b = \frac{ hA}{\rho Cp V}$

$b = \frac{ h}{\rho Cp Lc}$

$b = \frac{200}{8933*385*0.005}$

b = 0.01163 s^{-1}

putting value in equation 1

$\frac{25-20}{100-20} = e^{-0.01163t}$

solving for t we get

t = 4.0 min

6 0

3 years ago