Name: ___________________________
Date: _____________
Physics I H
Mr. Tiesler
Solutions to Physics Toolkit Homework Problems 6-10
6.) An airplane travels at 950 km h. How long does it take to travel 1.00 km?
Use the speed of the airplane to convert the travel distance into a time.
 1 h  3600 s 

  3.8 s
 950 km  1 h 
1.00 km 
7.) A typical atom has a diameter of about 1.0 10 10 m. (a) What is this in inches?
(b) Approximately how many atoms are there along a 1.0-cm line?


(a)
1.0 1010 m  1.0 1010 m  39.37 in 1 m   3.9 109 in
(b)
1.0 cm  
1 m  1 atom 
8

  1.0 10 atoms
10
 100 cm  1.0 10 m 
8.) Express the following sum with the correct number of significant figures:
1.80 m  142.5 cm  5.34 10 5 m.
To add values with significant figures, adjust all values to be added so that their units are all the same.
1.80 m  142.5 cm  5.34 105  m  1.80 m  1.425 m  0.534 m  3.759 m  3.76 m
When adding, the final result is to be no more accurate than the least accurate number used. In
this case, that is the first measurement, which is accurate to the hundredths place.


9.) A light-year is the distance light travels in one year at speed  3.00  108 m s . (a) How
many meters are there in 1.00 light-year? (b) An astronomical unit (AU) is the average distance
from the Sun to Earth, 1.50 108 km. How many AU are there in 1.00 light-year? (c) What is the
speed of light in AU h?



(a)
1.00 ly  2.998 108 m s 3.156 107 s  9.46 1015 m
(b)
 9.462  1015 m   1 AU 
4
1.00 ly  

  6.3110 AU

11
 1.00 ly   1.50  10 m 
(c)
 2.998 10
8
  1.501AU
10
ms 
11
 3600 s 

  7.20 AU h
m  1 hr 
10.) Estimate how long it would take one person to mow a football field using an ordinary home
lawn mower. Assume the mower moves with a 1 km h speed, and has a 0.5 m width. The
dimensions of an NFL field are 120 yd x 53.33 yd.
An NCAA-regulation football field is 360 feet long (including the end zones) and 160 feet wide, which is
about 110 meters by 49 meters, or 5,390 m2. The mower has a cutting width of 0.5 meters.
Thus the distance to be walked is
𝑑=
𝐴𝑟𝑒𝑎
5,390 𝑚2
=
= 10,780 𝑚 = 10.78 𝑘𝑚
𝑊𝑖𝑑𝑡ℎ
0.5 𝑚
At a speed of 1 km/hr, then it will take about 10.78 h to mow the field.