Calculate speed 5 meters from the end of path

[gijoel]

Homework Statement

A wheelchair is pushed from the start to the finish from its resting phase and maintains a steady speed of 2m/s as the wheelchair travels to its destination, which is 25 m from the start. It takes 80.seconds to push the wheelchair from the start to the finish. What is the wheelchair's instantaneous speed when the wheelchair is 5m away from the end? (Forgive the crude drawing)

Homework Equations

V= d/t
Cir = 2 pi r

The Attempt at a Solution

There's one of two possible solutions. the speed is 2m/s because the question states that the wheelchair maintains a speed of 2m/s as its speed. But that doesn't sound quite right to me

Considering that the path is circular from the start to the finish. And the start and finish areas are 25 meters away from each other then the circular path is

Cir = 2 pi r
= 25 pi
= 79 meters long

Therefore we need to know the speed at 74 meters.

I could then say that V=d/t
so V = 79meter/80. seconds
= 0.99 m/second

But that doesn't seem to make sense. Am I over thinking this here?

 

[HallsofIvy]

I don't understand what your question is. The problem says "A wheelchair ... maintains a steady speed of 2m/s" and then you ask "What is the wheelchair's instantaneous speed when the wheelchair is 5m away from the end?" Uhhh- 2 m/s? If an object has a constant speed then that is its "instantaneous speed".

 

[gijoel]

I thought as much. I'm just overthinking it. Thanks for your help.

 

[haruspex]

I don't understand what your question is. The problem says "A wheelchair ... maintains a steady speed of 2m/s" and then you ask "What is the wheelchair's instantaneous speed when the wheelchair is 5m away from the end?" Uhhh- 2 m/s? If an object has a constant speed then that is its "instantaneous speed".

While that is all true, the question still makes no sense. At 2m/s for 80 seconds it should cover 160m, yet the start and finish are only 25m apart and the path is supposed to be along a circular arc. Even two complete circles does not quite get to 160m.

Gojoel, are you sure you have stated the question exactly as given to you?

 

[gijoel]

Path is along the circular path. And I've pretty much stated the question as is. That's why I didn't get it. I think the answer is 2m/s and someone stuffed up. I'll check it out.

 

[chapp]

Path is along the circular path. And I've pretty much stated the question as is. That's why I didn't get it. I think the answer is 2m/s and someone stuffed up. I'll check it out.

Hi, i am doing the exact same assignment too! and am just as stuck on this question. I also assumed that the instant speed is 2m/s as its constant. The question has a lot of uncertainty and i think we need to state that in our answer.

 

[haruspex]

Hi, i am doing the exact same assignment too! and am just as stuck on this question. I also assumed that the instant speed is 2m/s as its constant. The question has a lot of uncertainty and i think we need to state that in our answer.

I can think of one small change which would make it a valid question: what is the instantaneous velocity 5m from the end?
(Assume a system of coordinates based on the start and finish points.)

 

[chapp]

I can think of one small change which would make it a valid question: what is the instantaneous velocity 5m from the end?
(Assume a system of coordinates based on the start and finish points.)

hmmm maybe, but unsure as the question doesn't address the velocity of the wheelchair and the next question after this asks us to comment on the wheelchairs velocity as its being pushed along the path, using justifications.

 

[haruspex]

hmmm maybe, but unsure as the question doesn't address the velocity of the wheelchair and the next question after this asks us to comment on the wheelchairs velocity as its being pushed along the path, using justifications.

If you post the subsequent questions they might provide some clues.

 

[chapp]

If you post the subsequent questions they might provide some clues.

These are the following questions:

3. Using justification(s), comment on the velocity of the wheelchair as it is being pushed along the circular path. (2 marks)

4. Express the average speed of the wheel chair during its movement from the Reception area to the Examination Room. Ensure that your final answer reflects the correct number of significant digits and units of measurement. (3marks)


5. Calculate the weight of the patient. Include definition(s), formula, correct number of significant digits and units of measurement in your answer. (4 marks)

6. Would it take a larger or a smaller pulling force on the wheelchair handles to stop the wheelchair within a certain period of time if the patient were 80 kg instead of 60 kg? Justify your answer.

 

[haruspex]

5. Calculate the weight of the patient. Include definition(s), formula, correct number of significant digits and units of measurement in your answer. (4 marks)

6. Would it take a larger or a smaller pulling force on the wheelchair handles to stop the wheelchair within a certain period of time if the patient were 80 kg instead of 60 kg? Justify your answer.

Those last two questions imply that you had been given information about the force used.
The last also implies that the speed is not constant. Rather, the wheelchair is brought to rest by a constant force.
This all points to the statement "maintains a steady speed of 2m/s" as being the garbage input, but I cannot guess what it was supposed to say.
Maybe a steady magnitude of force was applied.

 

[chapp]

Those last two questions imply that you had been given information about the force used.
The last also implies that the speed is not constant. Rather, the wheelchair is brought to rest by a constant force.
This all points to the statement "maintains a steady speed of 2m/s" as being the garbage input, but I cannot guess what it was supposed to say.
Maybe a steady magnitude of force was applied.

so the best answer for instantaneous would be '2m/s as the wheelchair is pushed at a steady speed, and to state in the answer the uncertainty of the question ?

 

[haruspex]

so the best answer for instantaneous would be '2m/s as the wheelchair is pushed at a steady speed, and to state in the answer the uncertainty of the question ?

I don't think there's any point in providing an answer. Instead, prove the question makes no sense.
(You will run into the same issue at Q4.)
You could say something worthwhile on Q3.
Btw, I only see one question in the OP, but your list in post #10 starts at Q3. What happened to Q2?

 

[chapp]

I don't think there's any point in providing an answer. Instead, prove the question makes no sense.
(You will run into the same issue at Q4.)
You could say something worthwhile on Q3.
Btw, I only see one question in the OP, but your list in post #10 starts at Q3. What happened to Q2?

the question i posted was question 2, "instantaneous speed" and question 1 was: Differentiate between ‘speed’ and ‘velocity’

 

[haruspex]

the question i posted was question 2, "instantaneous speed" and question 1 was: Differentiate between ‘speed’ and ‘velocity’

OK.
Do you know whether you and gijoel are in the same class? If not, maybe your teachers are getting this from some common source.

 

[chapp]

OK.
Do you know whether you and gijoel are in the same class? If not, maybe your teachers are getting this from some common source.

We are enrolled in the same class but we are at different campuses so we would have different teachers.

 

[gijoel]

Basically the question is define instantaneous speed and deduce what its value will be when the wheelchair is 5m away from the end. Justify your answer. Is there a difference between instantaneous speed and steady speed?

 

[CWatters]

While that is all true, the question still makes no sense. At 2m/s for 80 seconds it should cover 160m, yet the start and finish are only 25m apart and the path is supposed to be along a circular arc. Even two complete circles does not quite get to 160m.

Could be the circumference is somewhat greater than 160m. The 25m distance could be the straight line separation (a chord of the circle)? It fits the statement but doesn't really help solve the problem.

 

[CWatters]

Had another idea. See...

https://www.physicsforums.com/threads/instantaneous-speed.827441/#post-5197303

 

[gijoel]

So I got this from the lecturer.

I can see that many of you are still struggling with Section A Question 2 so I am rephrasing the question and hopefully it will start making more sense.

In this question, you are to assume that the wheelchair is moving at a steady speed of2m/s when it is 5m away from the Examination Room(end of the path). You need to now deduce if the Instantaneous speed will be equal to, less than or more than 2m/s and explain why. You do not need to use any formulas.

Hope the rest of the assessment is progressing well.
​

The path is 25m in length as well. So that would mean that the instantaneous speed is 2 m/s, when 5meters from the examination room. Because it is 2m/s at the instant it is 5 meters away from the examination room?

 

[haruspex]

you are to assume that the wheelchair is moving at a steady speed of2m/s when it is 5m away from the Examination Room(end of the path). You need to now deduce if the Instantaneous speed will be equal to, less than or more than 2m/s and explain why. You do not need to use any formulas.

Hmm...
Then I suggest the first thing is to consider how one would define instantaneous speed and steady speed.

The path is 25m in length as well.

So the 25 m is distance along the path, not a straight line.
I'm still not seeing any data which could lead to an answer to Q5.

 

[gijoel]

Oh that's easy : Patient is 60kg and the wheelchair is 8kg.

Patient's weight is 60kg x 9.8m/sec^2 = 588kgm/sec^2

600N to 1 significant digit

 

[gijoel]

Instantaneous speed is the speed at a particular point in time. Steady speed is when an object's instantaneous speed remains constant throughout it's journey.

Correct?

 

[haruspex]

Instantaneous speed is the speed at a particular point in time.

That doesn't get you very far. A proper definition would involve distance, time and limits. But the important one for this question is the next one:

Steady speed is when an object's instantaneous speed remains constant throughout it's journey.

Well, over some time interval. I think that gives you a basis for answering the question.

600N to 1 significant digit

Why only 1?

 

[gijoel]

Because 60kg is only at one significant digit

 

[haruspex]

Because 60kg is only at one significant digit

How would you write a value of 60kg if you wanted to indicate 2 sig digits?

 

[gijoel]

60.kg

 

[haruspex]

60.kg

That's not a notation I've ever seen.
Searching around on the net now, it seems there is no generally accepted standard. I see a convention that matches what you say, but I see another that says if trailing zeroes left of the (implied) decimal point are not significant then you need to use scientific notation.

 

[gijoel]

That's not a notation I've ever seen.

That's how we were taught to do it.

 

[haruspex]

That's how we were taught to do it.

How would you show 600 to 2 significant digits?

 

[CWatters]

Oh that's easy : Patient is 60kg and the wheelchair is 8kg.

Your original problem statement didn't mention the mass of the patient. As far as I can see 60kg is only implied by Q6 posted by "chap". Please post the exact problem statement next time. Thanks.

 

[gijoel]

How would you show 600 to 2 significant digits?

Rounded to the nearest tens, so 590N

 

[haruspex]

Rounded to the nearest tens, so 590N

No, that shows some number between 585 and 595 to two sig figs. I asked how you would show a value of 600 to two sig figs.

 

[gijoel]

60x10^1

 

[haruspex]

60x10^1

That's not consistent with the way you wrote 60 to 2 sig figs. Seems to me you'd have to write either 60.*10¹ or, better, the standard scientific notation 6.0*10².

 

[gijoel]

My mistake 6.0x 10^2

 

[barofsoap69]

I also have an assignment like this and you guys are confusing as

 

[barofsoap69]

These are the questions that are being asked:

1. Differentiate between ‘speed’ and ‘velocity’. (2 marks)
2. Define the term ‘instantaneous speed’ and deduce what its value will be when the wheelchair is 5m away from the Examination Room. Justify your answer. (3 marks)
3. Using justification(s), comment on the velocity of the wheelchair as it is being pushed along the circular path. (2 marks)
4. Express the average speed of the wheel chair during its movement from the Reception area to the Examination Room. Ensure that your final answer reflects the correct number of significant digits and units of measurement. (3marks)
5. Calculate the weight of the patient. Include definition(s), formula, correct number of significant digits and units of measurement in your answer. (4 marks)
6. Would it take a larger or a smaller pulling force on the wheelchair handles to stop the wheelchair within a certain period of time if the patient were 80 kg instead of 60 kg? Justify your answer. (3 marks)
7. Explain how Newton’s Third Law of Motion applies to the wheelchair as it is pushed along the corridor.
(3 marks)

 

[haruspex]

These are the questions that are being asked:

1. Differentiate between ‘speed’ and ‘velocity’. (2 marks)
2. Define the term ‘instantaneous speed’ and deduce what its value will be when the wheelchair is 5m away from the Examination Room. Justify your answer. (3 marks)
3. Using justification(s), comment on the velocity of the wheelchair as it is being pushed along the circular path. (2 marks)
4. Express the average speed of the wheel chair during its movement from the Reception area to the Examination Room. Ensure that your final answer reflects the correct number of significant digits and units of measurement. (3marks)
5. Calculate the weight of the patient. Include definition(s), formula, correct number of significant digits and units of measurement in your answer. (4 marks)
6. Would it take a larger or a smaller pulling force on the wheelchair handles to stop the wheelchair within a certain period of time if the patient were 80 kg instead of 60 kg? Justify your answer. (3 marks)
7. Explain how Newton’s Third Law of Motion applies to the wheelchair as it is pushed along the corridor.
(3 marks)

And your attempts at answers are?

 

[barofsoap69]

Section A (20 marks)

1. Differentiate between ‘speed’ and ‘velocity’. (2 marks)
The difference between speed and velocity is that; speed is a scalar quantity that refers to the rate at which an object covers a distance regardless of its speed, whereas velocity is a vector quantity that refers to the rate at which an objects position changes (https://www.physicsforums.com/file:///D:/Garcia/Desktop/CQU%20Courses/Semester%202/MEDI11002/S0271038.docx#_ENREF_1 ).

2. Define the term ‘instantaneous speed’ and deduce what its value will be when the wheelchair is 5m away from the Examination Room. Justify your answer. (3 marks)
-
3. Using justification(s), comment on the velocity of the wheelchair as it is being pushed along the circular path. (2 marks)
The velocity of the wheelchair is not in a straight pathway it is in a semicircular direction from the reception area to the examination room (https://www.physicsforums.com/file:///D:/Garcia/Desktop/CQU%20Courses/Semester%202/MEDI11002/S0271038.docx#_ENREF_1 ).
4. Express the average speed of the wheel chair during its movement from the Reception area to the Examination Room. Ensure that your final answer reflects the correct number of significant digits and units of measurement. (3marks)

https://www.physicsforums.com/file:///C:/Users/Garcia/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png

https://www.physicsforums.com/file:///C:/Users/Garcia/AppData/Local/Temp/msohtmlclip1/01/clip_image004.png

https://www.physicsforums.com/file:///C:/Users/Garcia/AppData/Local/Temp/msohtmlclip1/01/clip_image006.png

https://www.physicsforums.com/file:///C:/Users/Garcia/AppData/Local/Temp/msohtmlclip1/01/clip_image008.png

∴ The average speed of the wheelchair is 31meters per second (https://www.physicsforums.com/file:///D:/Garcia/Desktop/CQU%20Courses/Semester%202/MEDI11002/S0271038.docx#_ENREF_1 ).

5. Calculate the weight of the patient. Include definition(s), formula, correct number of significant digits and units of measurement in your answer. (4 marks)
-
6. Would it take a larger or a smaller pulling force on the wheelchair handles to stop the wheelchair within a certain period of time if the patient were 80 kg instead of 60 kg? Justify your answer. (3 marks)
-
7. Explain how Newton’s Third Law of Motion applies to the wheelchair as it is pushed along the corridor. (3 marks)
Newton’s third law of motion is applied to the wheel chair as it is being pushed down the corridor as an external force is needed to move the wheelchair that is stationary to be in a state of motion (https://www.physicsforums.com/file:///D:/Garcia/Desktop/CQU%20Courses/Semester%202/MEDI11002/S0271038.docx#_ENREF_1 ) as also quoted; “When one object exerts a force on another, the second object exerts an equal and opposite force on the first object” (https://www.physicsforums.com/file:///D:/Garcia/Desktop/CQU%20Courses/Semester%202/MEDI11002/S0271038.docx#_ENREF_1 ).

 

[jbriggs444]

Section A (20 marks)

1. Differentiate between ‘speed’ and ‘velocity’. (2 marks)
The difference between speed and velocity is that; speed is a scalar quantity that refers to the rate at which an object covers a distance regardless of its speed, whereas velocity is a vector quantity that refers to the rate at which an objects position changes (https://www.physicsforums.com/file:///D:/Garcia/Desktop/CQU%20Courses/Semester%202/MEDI11002/S0271038.docx#_ENREF_1 ).

You quote "Falconi and Reshmi" a number of times, but the link is broken. You are expected to show your own work, not to produce references to someone else's.

In the passage above, the definition of speed mentions "regardless of its speed". That amounts to a circular definition. Possibly some other word was intended. Maybe "direction"?

 

[barofsoap69]

The reference is from the lecturer (video), I'm showing where i got the information from to prove it's not bull. The final answer is; "The difference between speed and velocity is that; speed is a scalar quantity that refers to the rate at which an object covers a distance regardless of its speed but time, whereas velocity is a vector quantity that refers to the objects speed and direction of motion "

 

[barofsoap69]

The only questions that I do not understand are;
2. Define the term ‘instantaneous speed’ and deduce what its value will be when the wheelchair is 5m away from the Examination Room. Justify your answer. (3 marks)

and

5. Calculate the weight of the patient. Include definition(s), formula, correct number of significant digits and units of measurement in your answer. (4 marks)

 

[haruspex]

The velocity of the wheelchair is not in a straight pathway it is in a semicircular direction from the reception area to the examination room

Nonsense statement. A velocity cannot have a curved direction, that doesn't mean anything. The velocity can change with time so as to produce a semicircular path.

‘instantaneous speed’ and deduce what its value will be when the wheelchair is 5m away from the Examination Room.

You didn't post an answer to this.

The average speed of the wheelchair is 31meters per second

I do not begin to see how that could follow from the information given. Do you mean 3.1?
If you want any useful responses, you will need to take the trouble to copy out all the working and post it. None of your links work for me.

 

[jbriggs444]

The reference is from the lecturer (video), I'm showing where i got the information from to prove it's not bull. The final answer is; "The difference between speed and velocity is that; speed is a scalar quantity that refers to the rate at which an object covers a distance regardless of its speed but time, whereas velocity is a vector quantity that refers to the objects speed and direction of motion "

And, as I pointed out, that answer is flatly wrong.

 

[William White]

This is a perfect example of a physics forum thread (and it happens all the time) where people who are supposed to be trying to help are deliberately making something more difficult.

Bending over backwards to be as abstract and difficult as possible (so as not to give a hint of an answer) is not teaching; its the opposite of teaching; and has the opposite effect of teaching; and its not in the spirit of education. Yes, telling the answer is not a good idea. Coaxing is a good idea. Being contrary is not a good idea.If somebody is confused about the difference between speed and velocity; just tell them what the bloody difference is!Speed has a magnitude. You can say you are driving with a speed of 80 mph

Velocity has a magnitude and a direction. You can say you are driving with a velocity of 80 mph northwards.

 

[jbriggs444]

This is a perfect example of a physics forum thread (and it happens all the time) where people who are supposed to be trying to help are deliberately making something more difficult.

Refer to post #41. Coaxing did not work.

 

[William White]

sure, I get that.

What I don't like is deliberate obfuscation; it's horrible.

Good teachers don't do that. And this is about teaching.

Several posts bickering about significant figures? Why? The poor kid had trouble understanding the concept. Just explain it rather than making post after post, the end result of which is to make something that should be easy, very difficult! I understand these things, and when I read the help here I end up being confused. God help the kid that doesn't understand.

Why not just define significant figures and say why they are important?

 

[William White]

Calculate the weight of the patient. Include definition(s), formula, correct number of significant digits and units of measurement in your answer. (4 marks)

The point about significant figures is that you should not give an answer with unjustified accuracy.

The answer is given to the same number as significant figures as the lowest number of figures given in the data.

So, if a box had a mass of 8 kg and the acceleration due to gravity is given as 9.81 m/s^2 then the weight of the box can only be given to ONE sig figure. Becaus the mass is only given to one figure.

If the box had a mass of 8.00kg you can give the answer to 3 sig figures
If the box had a mass of 8.000kg you can give the answer to 3 sig figures. Why only 3? Because the acceleration due to gravity is only given to 3 sig figures. You have to use the lowest number of sig figures from the data.
What if the box was 80 kg and acceleration is 9.81 m/s^2 ? The least number of sig figures is now two.

The weight is 80kg x 9.81m/s^2 = 784.8 N

You should write this as

A) 780 N (to two sig figures) (because mass is given to two sig figures)

or

B) 7.8 x 10^2 N (because mass is given to two sig figures)Both are correct (be sure if you use method A, to write in brackets (as I have done) the number of sig figures so that the 0 obviously seen as not significant. I think (A) looks neater, for a final answer and less fussy than (B); but B is useful in calculations)

Sig figures are a constant source of pain; and sometimes counter intuitive and a headache.

If you measure an angle, to the nearest angle, with your protractor you can write

–1° (1 sig figure)
or
359° (3 sig figures).

both are correct, but one looks like it is 3 times more accurate than the other, which it is not! You would not be justified making 1° into 1.00°; nor rounding 359° to 400° (or 0°)! Both would be very wrong. You need to make an educated decision about what number is justified and say that in the answer.And
Generally, zeros AFTER a decimal point are significant. Zeroes BEFORE are not. However, it is not easy! If your instrument is correct to five decimal places, which is more "accurate":

1.00001 Amps is 6 sig figures

0.00001 Amps is 1 sig figure

you could - as far as I am concerned - be justifed in saying that both are as accurate as each other - as long as you explain why you think that.Be sure to put in your answer WHY you have used the number of significant figures.

 

[Dale]

Closed pending moderation.