# I'm stcuk, sort of, not really, I need some resurance is all

• cooper43
In summary, the conversation discusses finding the amount of kinetic energy dissipated when a 250kg dog jumps into an empty boat and causes it to move at a speed of 1.75m/s away from the shore. The equation KE=1/2*m*v^2 is used and the attempt at a solution involves finding the kinetic energy before and after the jump, as well as considering the conservation of momentum. The final answer is found to be 2031.25.

## Homework Statement

Ive got another question that I think I might have failed at.

A dog weighing 250 kg jumps into an empty boat by the dock at a speed of 5m/s causing the boat to move away form the shore at 1.75m/s. Find the amount of kinetic energy dissipated.

KE=1/2*m*v^2

## The Attempt at a Solution

Before

KE=1/2*m*v^2
KE=(.5)(250kg)(5.0m/s)^2
KE(1)=3125

and after

KE=1/2*m*v^2
KE=(.5)(250)(1.75m/s)^2
KE(2)=382.813

KE1-KE2=2742.19

KE dissipated = 2742

So am I right?

Welcome to PF!

cooper43 said:
A dog weighing 250 kg jumps into an empty boat by the dock at a speed of 5m/s causing the boat to move away form the shore at 1.75m/s. Find the amount of kinetic energy dissipated.

Hi cooper43! Welcome to PF!

You need to include the KE of the boat, so put the mass of the boat = M, and use conservation of momentum.

Is conservation of momentum P=mv?

And hat do you mean Mass of the boat. Should I leave it as M or do I replace it with the mass of the dog

cooper43 said:
Is conservation of momentum P=mv?

Nooo … conservation of momentum is mvi + MVi = mvf + MVf

ie total momentum before = total momentum after …

it is always true for a collision.
And what do you mean Mass of the boat …

Now you're just being ridiculous.

tiny-tim said:
Nooo … conservation of momentum is mvi + MVi = mvf + MVf

ie total momentum before = total momentum after …

it is always true for a collision.

Now you're just being ridiculous.

LMAO! Well said!

As Tiny-Tim said, Final Momentum = Initial Momentum

Therefore,

mv = mv and you can work out your mass from there if necessary...

Okay, so i did the m1v1i + M2V2i = mvf + MVf
and M2=464.286

The KE of the dog is 3125

but I am not sure how to gt the other KE

should it be the dog+boat and the final velocity?

yes, the final value of the kinetic energy is found by considering the mass of the boat and the dog and the final velocity. They act as a single object (theoretically)

So its KE1=3125 and KE2=1093.75

what do i subtract from what?

wouldnt it normaly be KE1-KE2,,,but it would end up negative

cooper43 said:
So its KE1=3125 and KE2=1093.75

what do i subtract from what?

wouldnt it normaly be KE1-KE2,,,but it would end up negative

never mind, that made me look like a dumb ***

I figured it out

The amount of kinetic energy dissipated is KE=2031.25

## What do you mean by "stuck"?

When someone says they are "stuck," it typically means they are facing a problem or challenge and are having difficulty finding a solution or making progress.

## What do you mean by "sort of"?

The phrase "sort of" is often used to express uncertainty or hesitation in one's thoughts or feelings. In this context, it could mean that the individual is not fully committed to their current course of action or is unsure about their next steps.

## Why do you need reassurance?

Sometimes when facing a difficult situation, people may feel overwhelmed or doubt their abilities. Seeking reassurance is a way for individuals to gain confidence and validation in their thoughts and actions.

## How can I offer reassurance?

Reassurance can come in many forms, such as offering support and encouragement, providing helpful advice, or simply listening and understanding the individual's concerns. It is important to be empathetic and non-judgmental in offering reassurance.

## What can I do to help?

Depending on the situation, there are various ways to offer assistance. You can offer to brainstorm solutions together, provide resources or information that may be helpful, or simply be there to listen and offer emotional support. It is always best to ask the individual how you can best support them in their current situation.