Answered: 6 ft - Eat at Joe's 3 ft

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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Question

A pickup truck has a clean drag area C_D A of 35 ft².
Estimate the horsepower required to drive the truck at
55 mi/h (a) clean and (b) with the 3- by 6-ft sign in
Fig. P7.88 installed if the rolling resistance is 150 lbf
at sea level.

Expert Solution

Step 1

Given Data:

The drag area is C_DA = 35 ft2.
Velocity of truck is $V = 55 mi / h \times \frac{1.4672 ft / s}{mi / h} = 80.7 ft / s$ .
Rolling resistance is F_roll = 150 lbf.

Part (a)

The drag force can be calculated as,

$F = F_{r o l l i n g} + C_{D} A \frac{ρ}{2} V^{2} F = 150 lbf + 35 {ft}^{2} \times \frac{0.00238 slug / {ft}^{3}}{2} \times {(80.7 ft / s)}^{2} F = 150 lbf + 271.24 slug \cdot ft / s^{2} \times \frac{1 lbf}{1 slug \cdot ft / s^{2}} F = 421.24 lbf$

The horsepower required can be calculated as,

$P = F \times V P = 421.24 lbf \times 80.7 ft / s P = 33994.068 lbf \cdot ft / s \times \frac{1 hp}{550 lbf \cdot ft / s} P = 61.80 hp$

Thus, the power required is 61.80 hp.

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