
To find: the speed of each plane when 2 hours after first plane departs the planes are 3200 kilometers apart.

Answer to Problem 42E
The speed of the first plane is 880km/hr and second plane is 960 km/hr.
Explanation of Solution
Given:
Two planes start from Los angeles international airport and fly in opposite direction. The second plane starts ½ hour after the first plane, but its speed is 80 kilometers per hour faster.
Calculation:
Suppose two planes start from Los Angeles international airport and fly in opposite directions such that the second plane starts half hours after the first plane but its speed is 80 kilometers per hour faster.
Assume that the speed of first plane is
Since the second plane’s speed is 80 kilometers per hour faster then the first plane.
Therefore the speed of second plane is
Also, suppose the time at which first plane departs be
The distance formula is given by
Distance =speed
Therefore, the distance travelled by the first plane after 2 hours is
Also since the second plane starts half hour after the first plane, therefore the distance travelled by the second plane after 2 hours is
The distance between both the planes after 2 hours is 3200 km
Therefore,
Take the time ,
Speed of the second plane can be calculated as
Therefore, the speed of the first plane is 880km/hr and second plane is 960 km/hr.
Chapter 7 Solutions
Precalculus with Limits
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