How Far Will the Cart Travel at Increased Speeds?

[Scholar1]

Homework Statement

A cart is initially moving at 0.5 m/s along a track. The cart comes to rest after traveling 1 m. The experiment is repeated on the same track, but now the cart is initially moving at 1 m/s. How far does the cart travel before coming to rest.[/B]

Homework Equations

W=ΔKE[/B]
Ffd=1/2mv^2
d is proportional to velocity squared

The Attempt at a Solution

0.5^2=0.25
1^2=1
1/0.25=4m

The answer is 2 meters

 

[Ahmad Hossain]

what is problem there. Do you know the exact answer. I may try. But it is not as complex as you think. it is basic. The cart displacement depends on applied force.

 

[Scholar1]

I already posted the problem and my attempt at the solution. But I got the wrong answer.

 

[Ahmad Hossain]

yes i got the answer

 

[Ahmad Hossain]

It is not the energy problem

 

[Ahmad Hossain]

it is kinematics problem. Look there is only matter time. Ok

 

[Scholar1]

Explain..?

 

[Ahmad Hossain]

time is equal both cases. so time is 2s

 

[Scholar1]

That doesn't really help..?

 

[Ahmad Hossain]

Ok, of course, you need to know the basic physics. v=x/t...0.5=1/t...t=2s... for second case...x=vt----------v=1*2=2m

 

[Scholar1]

what is problem there. Do you know the exact answer. I may try. But it is not as complex as you think. it is basic. The cart displacement depends on applied force.

time is equal both cases. so time is 2s

Ok, of course, you need to know the basic physics. v=x/t...0.5=1/t...t=2s... for second case...x=vt----------v=1*2=2m

I do not believe you can just assume the times are the same.

 

[Ahmad Hossain]

you may forget, you use the same track...so common sense.

 

[Ahmad Hossain]

it is not so complex. Read the book...it is better

 

[Scholar1]

you may forget, you use the same track...so common sense.

That doesn't make sense at all... Thats like saying any two trains on the same track will stop in the same amount of time. You are completely ignoring other factors.

 

[Ahmad Hossain]

that's why i advice you read the book Tipler physics...it is very high level book...so you can find the answer. In forum i cannot explain all things in a short time ...i am also busy,,,,,,,,,I just give you the right answer...your conception you need to clear it...I cannot do it in a short time...may be you do not have deep knowledge in physics.so it can happen.

 

[Scholar1]

that why i advice you read the book Tipler physics...it is very high level book...so you can find the answer. In forum i cannot explain all things in a short time ...i am also busy,,,,,,,,,I just give you the right answer...your conception you need to clear it...I cannot do it in a short time...may be you do not have deep knowledge in physics.so it can happen.

I think it is best you let someone else help on this one. You are only telling me I do not understand physics instead of solving the question correctly. I already provided you the answer and then you just told me my answer again.

 

[Doc Al]

0.5^2=0.25
1^2=1
1/0.25=4m

The answer is 2 meters

Why do you think the answer is 2 meters?

I'd say that your initial answer of 4 m was correct.

 

[Scholar1]

Why do you think the answer is 2 meters?

Thanks for your reply. I actually thought the answer was 4m based on my work above. The answer key says the answer is 2m. Therefore I clearly am doing something wrong and need help. Hence I posted on this forum...

 

[Doc Al]

The answer key says the answer is 2m. Therefore I clearly am doing something wrong and need help.

Not necessarily. The answer key can be wrong.

The key is: what is the same between the two trails? The assumption must be that the retarding force and thus the acceleration is the same.

Which leads to your answer of 4 m. The faster car has 4 times the energy and thus 4 times the work must be done to stop it and thus 4 times the distance.

 

[Scholar1]

So you are saying I am correct?

 

[Doc Al]

time is equal both cases. so time is 2s

Why in the world would you think the time was the same? And where did you get 2 s?

 

[Doc Al]

So you are saying I am correct?

Yes.

 

[Scholar1]

Not necessarily. The answer key can be wrong.

The key is: what is the same between the two trails? The assumption must be that the retarding force and thus the acceleration is the same.

Which leads to your answer of 4 m. The faster car has 4 times the energy and thus 4 times the work must be done to stop it and thus 4 times the distance.

Yes.

Wonderful. Ahmad Hossain just trolled me for an hour and insulted me for no reason.

 

[Ahmad Hossain]

I think it is best you let someone else help on this one. You are only telling me I do not understand physics instead of solving the question correctly. I already provided you the answer and then you just told me my answer again.

Yes.

no, 4m is totally incorrect...because common sense

 

[Doc Al]

no, 4m is totally incorrect...because common sense

Please state your reasoning and calculation. "Common sense" is not a physics principle.

 

[Scholar1]

no, 4m is totally incorrect...because common sense

I do not think you understand physics and merely are a troll.

 

[Ahmad Hossain]

just you should go to you professor ask that I am wrong or he is wrong...I know something but it is not mean I know false.

 

[Ahmad Hossain]

Please state your reasoning and calculation. "Common sense" is not a physics principle.

you told me why 4m...

 

[Doc Al]

just you should go to you professor ask that I am wrong or he is wrong...I know something but it is not mean I know false.

We already know that you are wrong. Unless you show us your calculations to prove otherwise.

 

[Doc Al]

you told me why 4m...

I did and so did Scholar1. Show us where the mistake lies.

 

[Ahmad Hossain]

First read the question....I am mechanical engineer and I am working with motion...so he asked us that A cart has initial velocity is 0.5m/s and displacement 1m and the same track, the experiment do again and the cart velocity 1m/s and how far it moves? he mentions same track and the experiment do again...that is the mean key to understand the problem...in this question he only wants to know the displacement...first find out its time when it moves 1m...So v=X/t...0.5=1/t and t=2s... Now its initial velocity 1m/s and inital velocity can differ and it depends on your applied force...so you can travel same distance in a same time and initial velocity can differ. final answer x=vt...x=1*2 =2m

 

[Doc Al]

first find out its time when it moves 1m...So v=X/t...0.5=1/t and t=2s...

This calculation is incorrect. The speed is not constant. (Hint: Find the average speed.)

Now its initial velocity 1m/s and inital velocity can differ and it depends on your applied force...so you can travel same distance in a same time and initial velocity can differ. final answer x=vt...x=1*2 =2m

This is wrong. (For multiple reasons, including the same error made above.) You cannot just assume the the same time. Use physics!

 

[Ahmad Hossain]

I think it is best you let someone else help on this one. You are only telling me I do not understand physics instead of solving the question correctly. I already provided you the answer and then you just told me my answer again.

Not necessarily. The answer key can be wrong.

The key is: what is the same between the two trails? The assumption must be that the retarding force and thus the acceleration is the same.

Which leads to your answer of 4 m. The faster car has 4 times the energy and thus 4 times the work must be done to stop it and thus 4 times the distance.

EDIT: Sorry, posted my mistake. Can't figure out how to delete it!

what you do not understand.

This calculation is incorrect. The speed is not constant. (Hint: Find the average speed.)This is wrong. (For multiple reasons, including the same error made above.) You cannot just assume the the same time. Use physics!

I use same time because of his question and you can change initial velocity because you applied force is different.the box has same mass and the track is same...it is better you do the experiment. I am sure 100%...

 

[Doc Al]

I use same time because of his question and you can change initial velocity because you applied force is different.the box has same mass and the track is same...

What do you mean by "applied force"? The force that gives the car its initial speed? That is irrelevant. What matters is the force from the track, which is the same.

I am sure 100%...

But still wrong.