Question

Всадник проехал за первый час 8 км/ч, следующие 30 минут двигался 12 км/ч, последние 5 км шёл пешком со скоростью 5 км/ч.Определить среднюю скорось всадника на втором половине пути км/ч

Answer 1

t1=1ч
v1=8 км/ч
S1=8 км

t2=0,5ч
v2=12 км/ч
S2=6 км

t3=1 ч
v3=5 км/ч
S3=5 км

S=8+6+5=19 км - весь путь
S/2=9,5 км - длина половины пути

[9,5км] = S1+S2/4=8км + 1,5км - первая часть пути
[9,5км] =  S2*3/4+S3=4,5 км + 5км - вторая часть пути

v [cр 1/2] = (S1+S2/4)/(t1+(S2/4):v2)=(8+1,5)/(1+1,5/12)=8,(4) км/час - средняя скорость за первую половину пути
v [cр 2/2] = (S2*3/4+S3)/((S2*3/4):v2+t3)= (4,5+5)/(4,5/12+1)=6,(90) км/час- средняя скорость за вторую половину пути

ответ 6,(90) км/час

Answer 2

Calculation of Average Speed

To determine the average speed of the rider during the second half of the journey, we need to calculate the total distance covered and the total time taken during that period.

The rider traveled at a speed of 8 km/h for the first hour, then at a speed of 12 km/h for the next 30 minutes, and finally walked 5 km at a speed of 5 km/h.

Let's break down the calculations step by step:

1. Convert the time taken for each segment into hours: - The first hour is 1 hour. - The next 30 minutes is 0.5 hours. - The walking distance of 5 km is not relevant for this calculation.

2. Calculate the total distance covered during the second half of the journey: - The distance covered at a speed of 8 km/h is 8 km/h * 1 hour = 8 km. - The distance covered at a speed of 12 km/h is 12 km/h * 0.5 hours = 6 km.

3. Calculate the total time taken during the second half of the journey: - The total time taken is 1 hour + 0.5 hours = 1.5 hours.

4. Calculate the average speed: - Average speed = Total distance / Total time = (8 km + 6 km) / 1.5 hours = 14 km / 1.5 hours.

Therefore, the average speed of the rider during the second half of the journey is 9.33 km/h.

Please note that the walking speed of 5 km/h is not relevant for calculating the average speed during the second half of the journey.