At 8:00 a.m., someone took a boat with bamboo and went upstream. At 10:30 a.m., he found a bundle of bamboo falling into the river. He immediately turned around and went downstream to chase it. It took him 30 minutes to catch up with the bamboo pole. When did the bamboo pole fall into the water? 2. A group of infantry is advancing at a constant speed of 5.4 km / h. the correspondent runs from the end of the team to the head of the team and immediately returns to the end of the team. If the correspondent's speed is 21.6 km / h, what is the length of the infantry line?

At 8:00 a.m., someone took a boat with bamboo and went upstream. At 10:30 a.m., he found a bundle of bamboo falling into the river. He immediately turned around and went downstream to chase it. It took him 30 minutes to catch up with the bamboo pole. When did the bamboo pole fall into the water? 2. A group of infantry is advancing at a constant speed of 5.4 km / h. the correspondent runs from the end of the team to the head of the team and immediately returns to the end of the team. If the correspondent's speed is 21.6 km / h, what is the length of the infantry line?

Let the speed of bamboo fall into the water be v. if the speed of the boat is V, then the velocity of the counter current (v-v.) and the velocity of the downstream (V + V.) will be (11-x) * v. after bamboo fall into the water, the boat will continue to move forward. (10.5-x) * (v-v.) the boat chased bamboo downstream for half an hour, which is 0.5 * (V + V.)