Distance travelled whilst decelerating

[gary32]

#29 did not answer any of the questions in #28. Potential energy is relevant, but the question was about total energy.

I think I've got it,

KE = 0.5 x Mass x Velocity²
KE = 15054400J

So that is the amount of energy dissipated when it comes to a stop so
height = energy / m x g
height = 15054400 / 80000 x 9.81 = 19.18m
using trig,
hyp (distance) = opp (height) / sin(8)
distance = 19.18/sin(8) = 137.8m

NOW, I know I have not implemented tractive resistance here, I am not sure where I would implement it?
What is Newtons/kg? I kind of figure if I implemented it with an acceleration/velocity it would be word done?

 

[voko]

You have computed the height assuming no resistance. But there is resistance. So the train performs some WORK to overcome it. How are the initial total energy and the final total energy are interrelated with work?

 

[gary32]

You have computed the height assuming no resistance. But there is resistance. So the train performs some WORK to overcome it. How are the initial total energy and the final total energy are interrelated with work?

Initial energy + Work energy = Final total energy?

What is Newtons per kg physically? to me, Newtons is a force, as in weight, as in, mass x gravity and then kg is a mass so to me i see it as mass x gravity / mass which is just gravity so its confusing.
How can I formulate N/Kg into work energy, I have searched the internet and cannot find a formula that uses Newtons mass and energy in it

 

[voko]

Initial energy + Work energy = Final total energy?

Correct.

What is Newtons per kg physically? to me, Newtons is a force, as in weight, as in, mass x gravity and then kg is a mass so to me i see it as mass x gravity / mass which is just gravity so its confusing.

You were able to use the coefficient to find the tractive resistance force earlier, why are you confused now?

How do you compute work when you know the force?

 

[gary32]

Correct.
You were able to use the coefficient to find the tractive resistance force earlier, why are you confused now?

How do you compute work when you know the force?

I calculated tractive resistance force as F = 80000 x 0.07 = 5600N
That is just a force, not work done?
I know work done is Force x Distance, but I don't have an actual distance other than the one I calculate in the end (and tractive resistance needs to be implemented before you work out the distance right?)

EDIT: Unless I am being plain stupid and Work done = Force x Some angle (sin8)?

 

[voko]

I calculated tractive resistance force as F = 80000 x 0.07 = 5600N
That is just a force, not work done?

Correct.

I know work done is Force x Distance

Correct, too.

but I don't have an actual distance other than the one I calculate in the end

So make it some unknown variable, and solve for it.

 

[gary32]

So make it some unknown variable, and solve for it.

You've lost me now

Please give me a clue or example,

 

[voko]

If force is F, and displacement is s, what is the work of the force?

If the displacement is s along the gradient angle a, what is the elevation in the end? And what is the corresponding potential energy?

 

[gary32]

If force is F, and displacement is s, what is the work of the force?

If the displacement is s along the gradient angle a, what is the elevation in the end? And what is the corresponding potential energy?

Work of the force is F x displacement?

If displacement is s along the gradient a,
The end elevation is Sin8 x s
Corresponding potential energy is 15054400J?

I still am lost, honestly, I am probably as dumb as it gets when it comes to mechanics, you need to dumb things down to my level

 

[voko]

Work of the force is F x displacement?

Use the symbol $s$ for displacement.

If displacement is s along the gradient a,
The end elevation is Sin8 x s
Corresponding potential energy is 15054400J?

This cannot be a number, because the end elevation is $s \cdot \sin a$, where $s$ is unknown. So you have to write that down as a formula.

 

[gary32]

Use the symbol $s$ for displacement.



This cannot be a number, because the end elevation is $s \cdot \sin a$, where $s$ is unknown. So you have to write that down as a formula.

So what now? Also, what was the principle I used to initially work the problem out?

 

[voko]

So what now?

Write the work-energy equation in terms of known and unknown variables, and solve it.

Also, what was the principle I used to initially work the problem out?

Not sure whether there is a particular name to it. FBD analysis and first principles of motion, perhaps.

 

[gary32]

Write the work-energy equation in terms of known and unknown variables, and solve it.

Not sure whether there is a particular name to it. FBD analysis and first principles of motion, perhaps.

There are 2 unknown variables (from what I can see) so I can't see a way for solving it,
I will have to not submit this work and not get the mark as I am away until the day it needs submitting.

Thanks for everyones help, it has been appreciated.

 

[voko]

Which two unknowns do you think you have here?

 

[gary32]

Which two unknowns do you think you have here?

Work done is unknown because that's what I am trying to find and s appears to be unknown, i know you've said s sin but that means nothing to me. Of course this is solvable but I don't have a clue how

 

[voko]

Work depends on s. Just write that down as a formula. Then plug that formula into the energy-work equation. That will eliminate the work as an unknown.

 

[gary32]

Work depends on s. Just write that down as a formula. Then plug that formula into the energy-work equation. That will eliminate the work as an unknown.

Work = F x s
Energy-work equation = F d = (1/2 mv²) - (1/2 mv²)

Energy-work equation = F d = (1/2 x 80000 x 0²) - (1/2 x 80000 x 19.4²)

= -15054400J

d = W/F
d = -15054400J/what force?

 

[voko]

Work = F x s
Energy-work equation = F d = (1/2 mv²) - (1/2 mv²)

This is not what you had in #33.