Question

Средняя скорость движения пешехода на всем пути v = 4 км/ч. Первую половину пути он шел равномерно со скоростью v1 = 3 км/ч. Найдите скорость равномерного движения пешехода на второй половине пути.

Answer 1

Vср=(S1+S2)/(t1+t2), т.к. S1=S2, t1=S1/v1, t2=S2/v2=S1/v2, тогда Vср=2S1/(S1/v1+S1/v2)=2v1*v2/(v1+v2), 4=2*3*v2/(3+v2). 2(3+v2)=3v2. v2=6 км/ч

Answer 2

Calculation of the Pedestrian's Speed on the Second Half of the Path

To find the speed of the pedestrian on the second half of the path, we can use the formula for average speed:

Average Speed = Total Distance / Total Time

Let's assume that the total distance of the path is d kilometers. Since the pedestrian walked the first half of the path with a speed of 3 km/h, the distance covered in the first half is d/2 kilometers.

The time taken to cover the first half of the path can be calculated using the formula:

Time = Distance / Speed

So, the time taken to cover the first half of the path is (d/2) / 3 hours.

Now, let's calculate the time taken to cover the second half of the path. Since the pedestrian's average speed for the entire path is 4 km/h, the time taken to cover the entire path is d / 4 hours.

The time taken to cover the second half of the path can be calculated by subtracting the time taken for the first half from the total time:

Time for Second Half = Total Time - Time for First Half

Substituting the values, we get:

Time for Second Half = (d / 4) - ((d/2) / 3)

Now, we can calculate the speed on the second half of the path using the formula:

Speed = Distance / Time

The distance covered on the second half of the path is d/2 kilometers. Substituting the values, we get:

Speed = (d/2) / ( (d / 4) - ((d/2) / 3) )

Simplifying the expression, we get:

Speed = (3d) / (4d - 6d)

Simplifying further, we get:

Speed = (3d) / (-2d)

Finally, we can simplify the expression to find the speed on the second half of the path:

Speed = -3/2 km/h

Therefore, the speed of the pedestrian on the second half of the path is -3/2 km/h.

Note: The negative sign indicates that the pedestrian is moving in the opposite direction on the second half of the path.