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3 years ago

Why the colours of school buses are yellow

2 answers:

5 0

Answer: The color of buses are yellow because when the bus is coming you have a more likely chance to notice it cause its a bright color. IT also attracts more attention. Its brighter then any other color.

Explanation:

Nesterboy [21]3 years ago

3 0

Answer:

because it attracts attention and is noticed quickly in peripheral vision

Explanation:

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A 5-mm-thick stainless steel strip (k = 21 W/m•K, rho = 8000 kg/m3, and cp = 570 J/kg•K) is being heat treated as it moves throu

Drupady [299]

Answer:

The temperature of the strip as it exits the furnace is 819.15 °C

Explanation:

The characteristic length of the strip is given by;

$L_c = \frac{V}{A} = \frac{LA}{2A} = \frac{5*10^{-3}}{2} = 0.0025 \ m$

The Biot number is given as;

$B_i = \frac{h L_c}{k}\\\\B_i = \frac{80*0.0025}{21} \\\\B_i = 0.00952$

$B_i$ < 0.1, thus apply lumped system approximation to determine the constant time for the process;

$\tau = \frac{\rho C_p V}{hA_s} = \frac{\rho C_p L_c}{h}\\\\\tau = \frac{8000* 570* 0.0025}{80}\\\\\tau = 142.5 s$

The time for the heating process is given as;

$t = \frac{d}{V} \\\\t = \frac{3 \ m}{0.01 \ m/s} = 300 s$

Apply the lumped system approximation relation to determine the temperature of the strip as it exits the furnace;

$T(t) = T_{ \infty} + (T_i -T_{\infty})e^{-t/ \tau}\\\\T(t) = 930 + (20 -930)e^{-300/ 142.5}\\\\T(t) = 930 + (-110.85)\\\\T_{(t)} = 819.15 \ ^0 C$

Therefore, the temperature of the strip as it exits the furnace is 819.15 °C

5 0

3 years ago

A cylindrical specimen of a titanium alloy having an elastic modulus of 107 GPa (15.5 × 106 psi) and an original diameter of 3.7

Keith_Richards [23]

Answer:

the maximum length of specimen before deformation is found to be 235.6 mm

Explanation:

First, we need to find the stress on the cylinder.

Stress = σ = P/A

where,

P = Load = 2000 N

A = Cross-sectional area = πd²/4 = π(0.0037 m)²/4

A = 1.0752 x 10^-5 m²

σ = 2000 N/1.0752 x 10^-5 m²

σ = 186 MPa

Now, we find the strain (∈):

Elastic Modulus = Stress / Strain

E = σ / ∈

∈ = σ / E

∈ = 186 x 10^6 Pa/107 x 10^9 Pa

∈ = 1.74 x 10^-3 mm/mm

Now, we find the original length.

∈ = Elongation/Original Length

Original Length = Elongation/∈

Original Length = 0.41 mm/1.74 x 10^-3

Original Length = 235.6 mm

5 0

3 years ago

Two cars are traveling on level terrain at 55 mi/h on a road with a coefficient of adhesion of 0.75. The driver of car 1 has a 2

Vlad1618 [11]

Answer:

0.981

Explanation:

velocity of cars ( v1 , v2 ) = 55 mi/h

coefficient of adhesion ( u ) = 0.75

Reaction time of driver of car 1 = 2.3 -s

Reaction time of driver of car 2 = 1.9 -s

breaking efficiency of car 2 ( n2 ) = 0.80

Determine the braking efficiency of car 1

First determine the distance travelled during reaction time ( dr )

dr = v * tr ------- ( 1 )

tr ( reaction time )

v = velocity

note : 1 mile = 1609 m , I hour = 60 * 60 secs

back to equation 1

for car 1

dr1 =( 55 * 2.3 * 1609 ) / ( 60 * 60 )

= 56.53 m

for car 2

dr2 = ( 55 * 1.9 * 1609 ) / ( 60 * 60 )

= 46.70 m

next we calculate the stopping distances ( d ) using the relation below

ds = d + dr

d = distance travelled during break

dr = distance travelled during reaction time

where : d = $\frac{v^2intial}{2ugn}$

for car 1

d1 = $\frac{(55)^2}{2*0.75*9.81* n1} * (\frac{1609}{3600} )^2$

∴ d1 = $\frac{41.10}{n1}$

for car 2

d2 = $\frac{(55)^2}{2*0.75*9.8*0.8} * (\frac{1609}{3600} )^2$

∴ d2 = 51.38

since the stopping distance for both cars are the same

d1 + dr1 = d2 + dr2

( 41.10 /n1 ) + 56.53 = 51.38 + 46.70

solve for n1

hence n1 = 0.981 ( braking efficiency of car 1 )

4 0

3 years ago

Using bearings will cause more friction. A.True B.False

anyanavicka [17]

(False) bearings reduce friction by using smooth balls lubricated with oil or grease that freely roll between a smooth inner and outer surface. The main concept of the ball bearing is that objects that roll past each other produce less friction than if the objects were sliding against each other.

5 0

3 years ago

The author uses the example of the flameless candle to illustrate that

krek1111 [17]

Answer:

I don't necessarily know the context of the text you are talking about, but a flameless candle could represent how there no more light in the author's life, which could represent a lack of happiness or a loss. Hope this helps!

Explanation:

4 0

3 years ago

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Why the colours of school buses are yellow​

Why the colours of school buses are yellow