To solve the problem, we need to find Julian's average speed, given that he started biking from a position behind the simulated biker at a speed of 20 km/h, and after 15 minutes, his position was reported as -214 km.
We can use the formula for average speed:
Average speed = total distance / total time
To find the total distance, we need to calculate the displacement of Julian from the initial position of -d (where d is the distance between Julian and the simulated biker when he started biking) to the position of -214 km after 15 minutes.
Displacement = final position - initial position
Displacement = (-214 km) - (-d) = d - 214 km
The total distance covered by Julian is equal to the absolute value of the displacement, since the direction of the motion does not matter when computing distance.
Total distance = |d - 214 km|
To find the total time, we need to convert 15 minutes to hours:
Total time = 15 minutes / 60 minutes/hour = 0.25 hours
Now we can substitute the values into the formula for average speed:
Average speed = total distance / total time
Average speed = |d - 214 km| / 0.25 hours
Since Julian was traveling at a constant speed of 20 km/h, we can also express the distance in terms of time:
Average speed = (20 km/h) x t / 0.25 hours
where t is the time Julian biked in hours.
Setting the two expressions for average speed equal to each other, we can solve for t:
|d - 214 km| / 0.25 hours = (20 km/h) x t / 0.25 hours
|d - 214 km| = 20 km/h x t
Solving for t:
t = |d - 214 km| / 20 km/h
Now we can substitute this expression for t into either expression for average speed:
Average speed = (20 km/h) x t / 0.25 hours
Average speed = |d - 214 km| / 0.25 hours
Substituting the expression for t:
Average speed = |d - 214 km| x 4 / |d - 214 km|
Simplifying:
Average speed = 80 km/h
Therefore, Julian's average speed so far has been 80 km/h.