Question

из одного пункта одновременно в противоположных направлениях отправляется пешеход со скоростью 5 км/ч и велосипедист со скоростью 12 км/ч. Через сколько часов расстояние между ними будет равно 51 км?

Answer 1

The question is about the time it takes for a pedestrian and a cyclist to move away from each other by 51 km, if they start from the same point and move in opposite directions with speeds of 5 km/h and 12 km/h, respectively. To answer this question, we need to use the formula for the relative speed of two objects moving in opposite directions:

$$v_{rel} = v_1 + v_2$$

where $v_{rel}$ is the relative speed, $v_1$ is the speed of the first object, and $v_2$ is the speed of the second object. In this case, the first object is the pedestrian and the second object is the cyclist, so we have:

$$v_{rel} = 5 + 12 = 17 \text{ km/h}$$

This means that the distance between them increases by 17 km every hour. To find the time it takes for them to be 51 km apart, we need to divide the distance by the relative speed:

$$t = \frac{d}{v_{rel}} = \frac{51}{17} = 3 \text{ hours}$$

Therefore, the answer is 3 hours. This is the same answer that is given by one of the web search results. Another web search result has a similar question, but with different speeds and distances. The third web search result has some examples of problems on motion in opposite directions.