The car drove the first 80 km at a speed of 100 km / h. Find the speed of the car in the last 60 km
| May 17, 2021 | education
The car drove the first 80 km at a speed of 100 km / h. Find the speed of the car in the last 60 km if the average speed along the entire path is 50 km / h.
The average speed of a car can be represented as a formula:
Vav. = S / t, where Vav. Is the average speed along the entire path (Vav. = 50 km / h), S is the entire distance traveled (S = S1 + S2), t is the total travel time (t = t1 + t2).
First section:
S1 = 80 km, t1 = S1 / V1, where V1 = 100 km / h.
Second section:
S2 = 60 km, t2 = S2 / V2.
Vav. = (S1 + S2) / (S1 / V1 + S2 / V2).
50 = (80 + 60) / (80/100 + 60 / V2).
50 = 140 / (0.8 + 60 / V2).
0.8 + 60 / V2 = 2.8.
60 / V2 = 2.
V2 = 60/2 = 30 km / h.
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