Example Problems Done in Class: - George Mason University



Example Problems Done in Class:

These are examples covering the topic: speed

1) Elena has a one hour commute to school and she lives 20 miles away. What is her average speed?

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2) How fast does the moon go around the Earth? The distance from the surface of the Earth to the moon is 238,800 miles and the radius of the Earth is 6367 km.

The average speed is the total distance traveled divided by the time it takes to travel that distance. We know that the moon takes one month (27 days to be precise) to make one full circle around the earth. The distance it travels is the circumference of the circle defined by its orbit. If we call the radius of the orbit R, then:

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3) How fast does the space shuttle go around the Earth? The altitude of the space shuttle in orbit is about 200 miles?. (ans. 17, 500 mph - try working this one out)

4) Practice for graphing motion. Let us follow Erica’s morning to school today:

i) Erica gets in her car and goes 30 mph for 5 minutes to the nearest stop sign

ii) She realizes she forgets something, makes an immediate U turn and goes 30 mph in the opposite direction (back home) for 5 minutes

iii) She searches for her textbook for 10 minutes in her house

iv) She then speeds at a constant speed of 100 mph for half an hour to make in time for class.

Draw a graph of velocity vs. time. Draw a graph of distance vs. time. How far away does Erica live? What was her average velocity?

Erica’s velocity vs. time graph would look like this:

[pic]

To find how far away she lives, we would just find the area under the graph. For this we would need to calculate the areas of the three shaded rectangles:

[pic]

Which is : [pic]

The distance vs. time plot would look like this:

[pic]

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