Question

Самокатчик первую половину времени движения от дома до работы ехал со скоростью 30км/ч, а вторую - со скоростью 15км/ч. С какой средней скоростью самокатчик проехал вторую половину пути?

Answer 1

Пусть всё время - 2t; тогда половина - t.

Vcp=весь путь / всё время =

(S1 + S2)/(2t)=(30*t + 15*t) / (2t)=t(30+15) / (2t)=(30+15)/2=22,5 км/ч.

Только ПРИ РАВНЫХ промежутках времени можно находить среднее арифметическое скоростей при нахождении средней скорости.

В других случаях нельзя.

Answer 2

Calculation of Average Speed

To calculate the average speed of the scooter rider during the second half of the journey, we need to know the distance covered during the entire journey. Unfortunately, the distance is not provided in the question. However, we can still calculate the average speed using the given information.

Let's assume that the total distance from home to work is D kilometers. Therefore, the first half of the journey covers D/2 kilometers, and the second half of the journey also covers D/2 kilometers.

During the first half of the journey, the scooter rider travels at a speed of 30 km/h. Therefore, the time taken to cover the first half of the journey can be calculated using the formula:

Time taken for the first half of the journey = Distance / Speed = (D/2) / 30 = D/60 hours

During the second half of the journey, the scooter rider travels at a speed of 15 km/h. Therefore, the time taken to cover the second half of the journey can be calculated using the formula:

Time taken for the second half of the journey = Distance / Speed = (D/2) / 15 = D/30 hours

Now, to calculate the average speed during the second half of the journey, we can use the formula:

Average Speed = Total Distance / Total Time

Since the total distance covered is D/2 kilometers and the total time taken is D/30 hours, we can substitute these values into the formula:

Average Speed = (D/2) / (D/30) = 30 km/h

Therefore, the scooter rider traveled the second half of the journey at an average speed of 30 km/h.

Please note that the above calculation assumes that the distance covered during the entire journey is the same for both halves. If the distance is different, the average speed will be different as well.