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?