Basic concept: Travel problem is to study the movement of objects, and it studies the relationship between the speed, time and travel of objects.

Basic formula: distance = speed × time; Distance ÷ time = speed; Distance/speed = time

Key question: determine the position in the journey.

Meeting problem: speed sum × meeting time = meeting distance (please write other formulas)

Meeting problem: (straight line): distance of A+distance of B = total distance.

Meeting problem: (ring): the distance of a+the distance of b = the circumference of the ring.

Follow-up question: Pursuit time = distance difference ÷ speed difference (write other formulas)

Follow-up questions: (straight line): distance difference = chaser distance-chased distance = speed difference x catching time.

Follow-up question: (circle): fast distance-slow distance = curve perimeter

Running water problem: downstream travel = (ship speed+water speed) × downstream time = (ship speed-water speed )× downstream time.

Downstream speed: ship speed+current speed = ship speed-current speed.

Still water speed: (downstream speed+upstream speed) ÷2 Water speed: (downstream speed-upstream speed) ÷2

Running water problem: the key is to determine the speed of the object, refer to the above formula.

Train crossing the bridge: the key is to determine the moving distance of the object, refer to the above formula.

Water problem: water speed+water speed ÷. Water speed: water speed-water speed ÷.

1. A warship and a cargo ship are heading from Port A to Port B, which is 100 km away. The speed of warships and cargo ships are 100 km/h and 20 km/h respectively, and warships are constantly patrolling in Port A and Port B (the time for patrolling to turn around is ignored). How long did it take for the cargo ship to meet the ship for the second time after it set off from Port A?

100 * 4/(100+20) =10/3 hours.

2. Two cars, A and B, leave from AB station respectively at the same time. They met for the first time at a distance of 90km from station A. After meeting, the two cars moved at the same speed, returned immediately after arriving at the other station, and met for the second time at a distance of 50km from station A to find the distance between the two stations AB.

When we first met, two cars, A and B, traveled 1 time, and car A traveled 90 kilometers.

When we met for the second time, two cars, A and B, * * * walked three full distances, and A car walked 90× 3 = 270 kilometers.

At the same time, there are two cars in shop A, which is 50 kilometers less.

The distance between the two stops is

(90× 3+50) ÷ 2 =160km