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katrin2010 [14]
3 years ago
14

How many seconds do you need to stop a car going 60 miles per hour, if the pavement is dry?

Engineering
1 answer:
Anna71 [15]3 years ago
7 0

Answer:

Roughly 4.6 seconds

Explanation:

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A driver is traveling at 90 km/h down a 3% grade on good, wet pavement. An accident
Paul [167]

Answer:

0.35

Explanation:

We resolve the component of the weight of the car along and perpendicular to the grade. We have mgsinФ and mgcosФ where Ф = angle of grade.

Now, the frictional force f = μN = μmgcosФ where μ = coefficient of friction

So, the net force along the grade is F = mgsinФ - μmgcosФ.

The work done by this force moving a distance, d along the grade is

W = (mgsinФ - μmgcosФ)d

This work equals the change in kinetic energy of the car. So ΔK = 1/2m(v₂² - v₁²) = W = (mgsinФ - μmgcosФ)d

1/2m(v₂² - v₁²) = (mgsinФ - μmgcosФ)d

1/2(v₂² - v₁²) = (gsinФ - μgcosФ)d

(v₂² - v₁²)/2d = (gsinФ - μgcosФ)

dividing through by gcosФ, we have

(v₂² - v₁²)/2dgcosФ = (gsinФ/gcosФ) - μgcosФ/gcosФ

(v₂² - v₁²)/2dgcosФ = tanФ -  μ

μ = tanФ - (v₂² - v₁²)/2dgcosФ

given that tanФ = 3% = 3/100 and 1 + tan²Ф = 1/cos²Ф, cosФ = 1/(√1 + tan²Ф) = 1/(√1 + (3/100)²) = 1/(√1 + (9/10000)) = 1/(√10000 + 9/10000) = 1/√(10009/10000) = 100/√10009 = 100/100.05 = 0.9995.

Also, given that v₁ = 90 km/h = 90 × 1000/3600 m/s = 25 m/s and v₂ = 45 km/h = 45 × 1000/3600 m/s = 12.5 m/s, d = 75 m and g = 9.8 m/s².

So, substituting the values of the variables into the equation, we have

μ = tanФ - (v₂² - v₁²)/2dgcosФ

μ = 3/100 - ((12.5 m/s)² - (25 m/s)²)/(2 × 75 m × 9.8 m/s² × 0.9995)

μ = 3/100 - ((156.25 m/s)² - (625 m/s)²)/1,469.265 m²/s²

μ = 3/100 - (-468.75 m²/s²)/1,469.265 m²/s²

μ = 3/100 + 468.75 m²/s²/1,469.265 m²/s²

μ = 0.03 + 0.32

μ = 0.35

So, theoretical friction  coefficient is 0.35

4 0
3 years ago
A column carries 5400 pounds of load and is supported on a spread footing. The footing rests on coarse sand. Design the smallest
Citrus2011 [14]

Answer:

Following are the responses to the given question:

Explanation:

7 0
2 years ago
How high of a column of sae 30 oil would be required to give the same pressure as 700 mm hg?
Rasek [7]

Hoiu-10,4000 mm.

<h3>Is positive pressure good for PC?</h3>
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7 0
1 year ago
Georgia Tech is committed to creating solutions to some of the world’s most pressing challenges. Tell us how you have improved o
Kaylis [27]

Answer:

Georgia Tech is committed to WGAR 53566 THE ANSWER IS JELLY IS KING AND THE JELLY IS KING AND  hope to improve the human condition in your community.

Explanation:

6 0
3 years ago
Does the location of a millimeter change the voltage or current of the circuit?
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Answer:

Yes, it does.

Explanation:

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