Answer:
The correct option is;
B. 50 km/h
Step-by-step explanation:
The information given in the question are;
The distance between the two cities = 140 km
The direction of motion of the first car = From A to B (left)
The direction of motion of the second car = From B to A
The time after which both cars meet = 1 hour
The time duration it takes after both cars meet for the second car to reach A = 35 minutes
The total time taken by the second car from city B to city A = The time it takes to meet the first car + The time it takes after meeting the first car to reach city A
∴ The total time taken by the second car from city B to city A = 1 hour + 35 minutes = 60 minutes + 35 minutes = 95 minutes
95 minutes = 95/60 hours = 1⁷/₁₂ hours = 1.58 hours
The speed of the second car = Distance/Time = 140 km/(1.58 hours) ≈ 88.42 km/h
Therefore, let the distance from A of the point the first car meet the second car = x
Therefore, we have;
The distance from B of the point both cars meet = (140 - x) km
Given that both cars meet after one hour, we have;
The distance travelled by the second car coming from city B, after one hour = (140 - x) km = Speed of the second car × 1 hour
88.42 km/h × 1 hour = 88.42 km = (140 - x) km
x = 140 - 88.42 ≈ 51.58 km
The distance from A of the point the first car meet the second car = x = 51.58 km
The speed of car A = (The distance from A of the point the first car meet the second car)/(Time it takes both cars to meet)
∴ The speed of the first car = 51.58 km/(1 hour)
The speed of the first car = 51.58 km/h ≈ 50 km/h (Rounding up to the nearest 10th).