S stands for the distance from the coast when we first met.
S stands for the distance from the shore when we met for the second time.
If the distance between two encounters is not the same shore, but the other shore, the second formula is used, and the first single shore formula is used.
Example:
Example: 1 A and B walk back and forth between A and B. A starts from A and B at the same time, and the first meeting point is 60 meters away from B. When B returns from A, he walks 10 meters and meets A for the second time. How many meters are a and b apart?
a、 150 B、 170 C、 180 D、200
Answer and analysis B. The total distance of the first encounter is S=(v A +v B) t 1, and the total distance of the second encounter is 3S=(v A +v B) t2. For A, the first meeting distance is S 1=S-60= v-A t 1, and the second meeting S2=2S- 10 =v-A t2, so S1/S2 = T1.
Two people, A and B, are swimming in a 30-meter-long swimming pool. A swims 37.5 meters per minute and B swims 52.5 meters per minute. At the same time, the two started from both ends of the pool, touched the wall and returned the same way, and so on. How many times did two people meet 1 min 50 seconds from the beginning, if the turning time is not counted?
a、2 B、3 C、4 D、5
Answer and analysis B. 1 minute 50s, the total distance they walked was (37.5+52.5) ×11/6 =165m. The total distance traveled by the two people at the nth meeting is (2n- 1)S≤ 165, and n=3.
Extended data:
Travel problem is a classic question in the mathematical operation part of civil service examination, which mainly studies the relationship between object speed, time and distance. Distance = speed × time, time = distance/speed, speed = distance/time. The above formula is the core formula of the travel problem. It is easy to find out the known quantities of speed, time and distance from the stem and then solve them with the core formula. Compared with the basic travel problem, the encounter problem involves two or more moving objects, and the process of solving the problem is more complicated. In the problem of meeting, there are meeting distance = speed and x time, time = meeting distance ÷ speed sum, and speed sum = meeting distance ÷ time.
Resources: Encountered Problems _ Baidu Encyclopedia