Answer:
- v(t) = 420/(t-3) -60
- v(7) = 45 km/h
- v(6) = 80 km/h
Step-by-step explanation:
When the second train leaves, the remaining distance between the trains is ...
... 600 km - (3 h)×(60 km/h) = 420 km
That distance will be covered at the speed of (60 +v) so the time it takes for the second train to cover that distance is ...
... 420/(60 +v)
The variable t represents the time since the first train left, so is 3 hours more than this time value. Hence ...
... t = 3 +420/(60 +v)
Solving for v, we have ...
... t -3 = 420/(60 +v) . . . . subtract 3
... 60 +v = 420/(t -3) . . . . multiply by (60+v)/(t -3)
... v = 420/(t -3) -60 . . . . subtract 60
For t = 7 ...
... v = 420/(7 -3) -60 = 105 -60 = 45
For t = 6 ...
... v = 420/(6 -3) -60 = 140 -60 = 80
