This exercise leads you through the reasoning used to calculate the distance fro
ID: 804345 • Letter: T
Question
This exercise leads you through the reasoning used to calculate the distance from a seismic station to an earthquake epicenter. But instead of two different seismic waves, let's see first how this works with two cars that start along a road at exactly the same time (see the figure on the next page). Both use cruise control set at 1 mile per minute (60 miles per hour), but the controls are not exactly the same. Car 1 covers each mile in exactly 60 seconds and Car 2 in 61 seconds. Because Car 1 arrives a second before Car 2 for each mile they travel, the delay between the arrival times of Car 1 and Car 2 increases at each mile marker. To see how this works, complete the illustration on the next page: (a) In each of the boxes to the right of Car 1 and Car 2, note the travel time (in seconds) needed to arrive at the different mileposts-the first one has been completed. (b) In the boxes at the bottom of the figure, indicate the delay time between arrival of Carl and Car 2 at each milepost.Explanation / Answer
Car 1 travel time:
Time(sec) 60 120 180 240 300 360 420
Distance (miles) 1 2 3 4 5 6 7
Car 2 travel time:
Time(sec) 61 122 183 244 305 366 427
Distance(miles) 1 2 3 4 5 6 7
Delay time(sec) 1 2 3 4 5 6 7
c. i. Since we know the velocity of car 1= 1mile/60 sec
Therefore distance travelled after 25 sec= Speed*time
=1mile/60sec*25 sec
=0.41 miles
ii. 45 sec after car 1
Therefore distance travelled=1 mile/60 sec*45
=0.75 miles
d.i If car 1 passed streetlight at 12:25
25 sec before car 2
The precise time of car 2=12:00
ii. 45 sec before car 2
Precise time of car 2=11:45
e. delay time between car 1 and 2= 1 minute and 15 sec=60 sec+15 sec=75sec
distance travelled=speed*time
=1mile/60sec*75 sec
=1.25 miles
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