# Dog walking on a raft on water then suddenly halting

• totallyclone
In summary, the question asks how far the dog will be from shore when it stops after walking 8.00m on a raft that is 20.0m from shore, with a mass of 40.0kg and no friction between the raft and water. This is a tricky question that involves considering the external force the dog applies to the raft and how it affects its movement.
totallyclone

## Homework Statement

A dog of mass 10.0kg is standing on a raft so that he is 20.0m from shore. He walks 8.00m along the raft towards shore and then halts. The raft has a mass of 40.0kg, and we can assume there is no friction between the raft and the water. How far is the dog from shore when he stops?

EK=1/2 mv2

## The Attempt at a Solution

This is a really tricky question and I'm not quite sure how to proceed. I know that when the dog halts, the raft moves forward towards the shore?

What's tricky about it? What external force would cause the raft to have a net movement?

phinds said:
What's tricky about it? What external force would cause the raft to have a net movement?

I find this question tricky because maybe I'm overthinking it...

I think the external force would be what the dog applies. Then suddenly stopping, transfers the energy to the raft causing it to more forward towards the shore?

totallyclone said:
I find this question tricky because maybe I'm overthinking it...

I think the external force would be what the dog applies. Then suddenly stopping, transfers the energy to the raft causing it to more forward towards the shore?

How is the dog external? What is the dog acting on that is external to the raft?

But I'm not sure how to calculate the distance the dog has moved or the velocity of the raft. Any suggestions?

I would approach this problem by first defining the system and identifying the relevant equations. In this case, the system includes both the dog and the raft, and the relevant equation would be the conservation of momentum. Since we are assuming no friction, we can also use the conservation of energy equation.

Using the conservation of momentum, we can set the initial momentum of the system (when the dog is at rest on the raft) equal to the final momentum of the system (when the dog halts and the raft moves forward).

Initial momentum = Final momentum
(10.0kg)(0m/s) + (40.0kg)(0m/s) = (10.0kg)(v) + (40.0kg)(v)

Solving for v, we get v = 0.4m/s, which is the velocity of the raft after the dog halts.

Next, we can use the conservation of energy equation to determine the distance the dog has moved. The initial energy of the system (when the dog is at rest on the raft) is equal to the final energy of the system (when the dog halts and the raft moves forward).

Initial energy = Final energy
(1/2)(10.0kg)(0m/s)^2 + (1/2)(40.0kg)(0m/s)^2 = (1/2)(10.0kg)(v)^2 + (1/2)(40.0kg)(v)^2

Solving for v again, we get v = 0.4m/s. This means that the dog has moved a total distance of 8.8m (8.0m + 0.4m) from its initial position of 20.0m from shore when it halts.

Therefore, the dog is 11.2m from shore when it stops. This calculation assumes that the dog and the raft are moving in a straight line towards the shore. If the motion is not in a straight line, more information would be needed to accurately calculate the distance from shore when the dog stops.

## 1. How is it possible for a dog to walk on a raft on water?

It's possible for a dog to walk on a raft on water because of the principles of buoyancy and surface tension. The raft displaces enough water to support the weight of the dog and the surface tension of the water keeps the raft from sinking.

## 2. Can any dog walk on a raft on water or are there specific breeds that are better suited?

Most dogs can walk on a raft on water, but there are certain breeds that may have an easier time due to their size, weight, and build. Dogs with webbed feet, such as Newfoundlands or Labradors, may also have an advantage.

## 3. Why does the raft suddenly halt while the dog is walking on it?

The raft may halt suddenly due to a change in the wind or current, causing the raft to shift direction. The dog's weight and movements can also affect the balance of the raft and cause it to stop abruptly.

## 4. Is it safe for a dog to walk on a raft on water?

It can be safe for a dog to walk on a raft on water, as long as certain precautions are taken. The raft should be stable and securely anchored, and the dog should be trained to stay on the raft and not jump off. A life jacket can also be worn for added safety.

## 5. Are there any potential dangers or risks associated with a dog walking on a raft on water?

There are some potential risks associated with a dog walking on a raft on water, such as the dog falling into the water or the raft overturning. It's important to supervise the dog and take proper safety measures to prevent any accidents from happening.

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