Question

С аэродрома вылетел вертолет со скоростью 210 км/ч. Через 2 ч с этого же аэродрома вылетел в след за вертолетом самолет, который через три часа после своего вылета перегнал вертолет на 840 км. Найдите скорость самолета.

Answer 1

Вертолёт был в пути 2+3 = 5 часов. За это время он пролетел 5*210 = 1050 км. Самолёт пролетел 1050+840 = 1890 км за 3 часа. Его скорость 1890:3 = 630 км/ч.

Answer 2

Problem Analysis

We are given the information that a helicopter took off from an airport with a speed of 210 km/h. Two hours later, an airplane took off from the same airport and caught up with the helicopter after flying for three hours, covering a distance of 840 km. We need to find the speed of the airplane.

Solution

Let's assume the speed of the airplane is x km/h.

The helicopter flew for 2 hours before the airplane took off. So, the distance covered by the helicopter in those 2 hours is given by:

Distance covered by the helicopter = Speed of the helicopter × Time taken by the helicopter = 210 km/h × 2 h = 420 km.

Now, let's consider the time it took for the airplane to catch up with the helicopter. The airplane flew for 3 hours and covered a distance of 840 km. Since the airplane caught up with the helicopter, the distance covered by the airplane is the same as the distance covered by the helicopter:

Distance covered by the airplane = Distance covered by the helicopter = 420 km.

Using the formula Distance = Speed × Time, we can write:

420 km = x km/h × 3 h.

Solving this equation for x, we find:

x = 420 km / 3 h = 140 km/h.

Therefore, the speed of the airplane is 140 km/h.

Answer

The speed of the airplane is 140 km/h.