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PHYS2014
Fall 2010
Benton
OSU Physics Dept.
1
Physics 2014: General Physics I
Homework Assignment 1: Solutions
Due:
Friday, 3 September 2010 at the beginning of your Recitation session.
Problems:
1. Convert the unit of furlongs/fortnight into meters/second.
Solution: Searching on Google for the term “furlong” reveals the fact a furlong is equal to one
eighth of a mile or:
1 furlong = 201.2 m .
Similarly, we find that 1 “fortnight” is equal to 2 weeks or 14 days:
1 fortnight
days
14
×
fortnight
hr
24
×
day
s
3600
hr
×
4
1,209,000 s
201.2 m
furlong
m
mm
1
1.66 10
0.166
fortnight
s
s
1,209,000 s
−
=
=
=
×
=
2. Explain why manholes and manhole covers are circular and not some other shape (e.g.
rectangular or oval).
Solution: If manholes and manhole covers were some shape other than circular, the manhole
covere could be turned on end and fall through the manhole …a possibly onto the head of the
worker below. This cannot happen with circular manholes and manhole covers.
3. Dr. Larry Pinsky, chairman of the Physics Department at the University of Houston, travels
more than anyone else I know. Last year he made 8 round trips to Geneva (home of CERN, the
European Particle Physics Center), 3 round trips to Tokyo (the Japanese KEK particle physics
laboratory is in Tsukuba, near Tokyo), 7 round trips to Chicago (Fermi National Accelerator
Laboratory), 5 round trips to New York (Brookhaven National Laboratory), 2 round trips to
London (apparently he likes English beer), and 1 round trip to each of the following cities:
Moscow, Buenos Aires, and New Delhi (for scientific conferences). Based on the table of round
trip distances below, find Dr. Pinsky’s average speed last year in m/s and in miles/hour. Why
might this estimate be on the low side (i.e. too small)? What was Dr. Pinsky’s average velocity
last year (assuming he spends every New Year at home)? (In case you’re wondering, a typical
jetliner flies at about 245 m/s or 550 miles/hour.)
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Fall 2010
Benton
OSU Physics Dept.
2
Table for Problem 3: Round trip distances between Houston, TX and major cities
visited by Dr. Pinsky last year.
City
Round Trip Distance
(km)
Round Trip Distance
(miles)
Geneva
16900
10500
Tokyo
21400
13260
Chicago
2980
1852
New York
4540
2820
Moscow
18920
11760
London
15200
9440
Buenos Aires
16320
10140
New Delhi
26924
16728
Solution: Total distance traveled in a year by Dr. Pinsky: 335,524 km or 208,352 miles.
There are 8760 hours in a year so Dr. Pinsky’s average speed is
335,524 km
km
38.3
hr
8760 hr
=
m
10.7
s
=
or 23.8 miles per hour. Since Dr. Pinsky spends every new year at home, all the
position vectors describing his travel will cancel out so that his average velocity is 0 m/s.
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