# Homework #3 Engineering Analysis and Introduction to Excel

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```					Phys 175: Introduction to Engineering                                       10 September 2008

Homework #3: Engineering Analysis and Introduction to Excel
Due: Wednesday 17 September 2008 at the beginning of class

1) Underline the number of significant digits
a) 0.00254
b) 29.8
c) 2001
d) 407.2
e) 0.031000
f) 2.006

2) Perform the calculations and report the correct number of significant figures
a) 5.64/1.9
b) 500./0.0025
c) (45.8-8.1)/1.922
d) 2π/2.50
e) (5.25 x 104)/(100 + 10.5)
f) v = 2.1(3.254) t +2.14 t2, where t = 3.2

3) A small parking lot is shown below. The center island has been planted with trees and grass.
Your job is to determine how much asphalt is required to pave the remainder of the parking lot.
All dimensions are given in Feet on the drawing. The Asphalt will be three inches thick. How
many cubic feet of asphalt should be ordered? How many cubic yards? [Hint: Area of a circle =
πr2]

4. Problem 1 on page 44 of course pack

5. Problem 4 on page 45 of course pack

6. Problem 11 on page 46 of course pack
Phys 175: Introduction to Engineering                                               10 September 2008

Excel Problems
• The problems should be worked in excel.
• Enter data above calculations and refer to these in equations. If possible, do not hard
wire numbers in formulas.
• Make sure that you label all rows and columns of data as appropriate.
• You are expected to complete this assignment independently.
• PAY ATTENTION TO UNITS!!!!!!!!!!!! Report units on all variables.
• You may need to do conversions.

7. The Wright brothers expected their airplane to lift a total weight (airplane and pilot) of 625
lbs. So after their 1900 glider did not produce enough lift they made measurements in a
homemade wind tunnel to determine the coefficients of lift for their wing design, as shown in the
table below.

Angle of
attack          CL (lift)
(degrees)
0             0.145
2.5             0.311
5.0             0.515
7.5             0.706
10.0             0.839

The equation for lift is:

L=kV2SCL

where

L = lift (lbs)                           k = Smeaton’s coefficient
V2 = velocity (mph)                      S = surface area of wing (ft2)
CL= lift coefficient

The Smeaton’s coefficient prior to the Wright brothers was calculated as 0.005; the Wright
brothers determined that it was 0.0033, and modern calculations show that it is 0.00257.
Calculate if there is enough lift for the different angles of attack for each value of the Smeaton’s
coefficient when S = 500 ft2 and V = 25 mph. Is the value of the Smeaton’s coefficient
important in this calculation? Calculate the percent difference from the modern value?

8. Problem 1 on page 319 of course pack

9. Problem 2 on page 319 of course pack
• First calculate the pressure of water in Pa, where P=ρgh
• Convert Pa to atm, where 1 atm = 101325 Pa
• Calculate the total pressure, where Ptotal = Pwater(atm) + Pbarometric(atm)
Phys 175: Introduction to Engineering                                            10 September 2008

•   Part b is the same problem, but the density of salt water is different, use ρ = 1050 kg/m3

10. Problem 3 on page 319 of course pack

11. Problem 5 on page 320 of course pack
• n is equal to the mass of ammonia gas divided by the molecular weight (units of “g mol”)
• calculate the volume for the case where the piston is at 2 cm
• T must be in degrees Kelvin (°K = °C + 273)
• For part b, you have two equations Vinitial = Acylinder*Lpiston-1 and Vfinal = Acylinder*Lpiston-2.
The area of the cylinder is the same. So combine the equations and solve for the final
volume.
• Now substitute that volume back into the ideal gas law and solve for T.

12. Problem 7 on page 322 of course pack
• F = mg
• T = F/2 (the opposing force is equally shared by the two cords)

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