Sci 10 Pre- IB
GPS
1. The video mentions a lot of numbers. The following questions are designed to help give
meaning to these numbers.
a) GPS satellites orbit at a height of 20 200 km above Earth’s surface. The radius of Earth is 6370
km. Draw a scale diagram of a GPS orbit and Earth.
b) GPS satellites move at 14 000 km/h. How does this speed compare to a car? Two times faster?
Twenty times? Two hundred times? Two thousand times?
c) The speed of light is 300 000 000 m/s. How long does it take for a radio signal, traveling at the
speed of light, to get from a GPS satellite to Earth’s surface?
d) How long does it take light to travel the length of a 30 cm ruler?
2. In this question you will be given some information about how far you are from three cities and
your goal is to find your location. This will model how GPS satellites locate a position.
Use the map of Canada handout and the clues below to locate the city that fits the criteria in the
clues.
a. You are located 2154 km from Vancouver.
b. You are also located 1879 km from Churchill Falls, Labrador.
c. You are also located 2464 km from Charlottetown, PEI.
d. Write down the name of the city you have located.
e. If you only knew how far you were from Vancouver, at which points on the map could you be
located? Label these points on the map.
f. If you only knew how far you were from Vancouver and Churchill Falls, at which points on the
map could you be located? Label these points on the map.
g. The GPS uses information from four satellites. What extra information does using this many
satellites provide?
3. We know that a GPS satellite orbits 20 200 km above the surface of earth. When a satellite is
over Halifax, Nova Scotia, how long will it take for the signal sent from the satellite to a GPS
receiver in Ottawa, Ontario?
 To calculate this, measure the distance from Halifax to Ottawa: _______cm.
 Use the scale and record the number of kilometers from Halifax to Ottawa: ___km
 Using Pythagoras’ Theorem calculate the distance the signal travels.
Satellite
dsignal
20 200 km
GPS receiver in
Ottawa

dground
Halifax
Knowing the speed of the signal, 3.00 x 105 km/s, and the distance the signal travels,
calculate the transit time for the signal to reach the receiver from the satellite.
4. Working backwards. Your GPS receiver has received signals from 3 satellites. The transit
time and location of each satellite is given below. Use your map and find the location of your
GPS receiver.
Satellite A is 20 200km above Fort McMurray, Alberta. t = 0.06821s
Satellite B is 20 200km above Iqaluit, NWT. t = 0.06764s
Satellite C is 20 200km above Thunder Bay, Ont. t = 0.06758s
Where is the GPS receiver?