Question

Из 2-ух пунктов расстояние между которыми 840км одновременно навстречу друг другу вышли 2 автомобиля. Один автомобиль проезжает это расстояние за 21 час, второй за 28ч. Через сколько часов произойдет встреча ?

Answer 1

1)100+10=110км/ч-скорость второго.2)100+110=210км/ч-скорость сближения.3)840:210=через 4 часа-они встретятся.ОТВЕТ: через 4 часа.

Answer 2

Problem Analysis

We have two cars that start simultaneously from two points that are 840 km apart and are moving towards each other. The first car covers this distance in 21 hours, while the second car covers it in 28 hours. We need to determine how many hours it will take for the cars to meet.

Solution

To find the time it takes for the cars to meet, we can use the concept of relative speed. The relative speed of two objects moving towards each other is the sum of their individual speeds.

Let's denote the speed of the first car as v1 and the speed of the second car as v2. Since the cars are moving towards each other, their relative speed is v1 + v2.

We know that the distance between the two points is 840 km. The time it takes for the cars to meet can be calculated using the formula:

Time = Distance / Relative Speed

Substituting the given values, we have:

Time = 840 km / (v1 + v2)

We are given that the first car covers the distance in 21 hours, so its speed can be calculated as:

v1 = Distance / Time = 840 km / 21 hours = 40 km/h

Similarly, the speed of the second car can be calculated as:

v2 = Distance / Time = 840 km / 28 hours = 30 km/h

Now that we have the speeds of both cars, we can calculate their relative speed:

Relative Speed = v1 + v2 = 40 km/h + 30 km/h = 70 km/h

Finally, we can calculate the time it takes for the cars to meet:

Time = Distance / Relative Speed = 840 km / 70 km/h = 12 hours

Therefore, the cars will meet after 12 hours.

Answer

The cars will meet after 12 hours.

Source:

-: '4 : ...', Sep 22, 2022