Solve Relative Motion: Boat, Wood + River Flow

In summary, the conversation discusses a problem involving a boat and a piece of wood moving in a river. The boat initially moves against the flow of the river, then turns around and catches up with the piece of wood. The problem is to determine the speed of the river. The conversation highlights the importance of thinking and using the right reference point to solve the problem. The correct answer is 3 km/h and the conversation concludes with the individual thanking the other for the helpful hint.
  • #1
Kamataat
137
0
Hi, I have this excercise that I've been trying to do for a couple of days now. Can anybody help me? Here's the question:

A boat is moving against the direction of flow of a river and meets a piece of wood that is moving along with the river. The boat continues against the flow of the river for another 30 minutes and then turns around. Moving at the same speed relative to the water as before, it catches up with the piece of wood 3km from the place where they met. What was the speed of the river?

Answer: 3 km/h.

I've tried setting up all sorts of equtions of motion relative to Earth (the place where they met), but haven't been successful at getting the right anwer. Should I set up the equations in terms of the point where the boat turns around?

- Kamataat
 
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  • #2
This is a problem that is to be solved by thinking, not by plugging into an equation.

From the reference point of the water surface, the piece of wood has NOT MOVED, has it?

From the reference point of the surface of the water, the boat has moved away for 1/2 an hour at a certain speed, and then returned at the same speed. Its the same distance at the same speed, so it must be the same time interval. It therefore must have been a full hour of travel for the boat.You got it from there?
 
  • #3
Yes, thank you. I was thinking of everything relative to the Earth when I should have just taken the boat's speed relative to the water as a hint that everything should be seen in relation to the water being stationary.
 

What is relative motion in the context of a boat, wood, and river flow?

Relative motion refers to the movement of an object in relation to another moving object or reference point. In this context, it refers to the motion of a boat and wood in relation to the flow of a river.

How can I solve for the relative motion of a boat, wood, and river flow?

To solve for relative motion, you will need to consider the velocities and directions of each object. You can use vector addition or the law of cosines to calculate the resultant velocity.

What factors affect the relative motion of a boat, wood, and river flow?

The relative motion of the boat, wood, and river flow is affected by the velocity and direction of each object, as well as any external forces such as wind or current.

What are some real-life applications of solving for relative motion?

Solving for relative motion is important in navigation, transportation, and engineering. It can also be applied in sports, such as calculating the velocity of a ball in relation to a moving player.

Are there any limitations to solving for relative motion?

There are some limitations to solving for relative motion, as it assumes that the objects are moving in a straight line and at a constant velocity. It also does not take into account any external factors that may affect the motion of the objects.

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