Please Can someone check my answer, ITS DONE, needs checking.

  • Thread starter livestrong136
  • Start date
In summary, the two trains are separating at a rate of 72.1 km/h after 1 hour of travel and 2 hours of travel. This was found by taking the derivative of the Pythagorean theorem function and simplifying to get a constant rate of separation.
  • #1
livestrong136
25
0
1. Two trains start from the same point at the same time, one going east at a rate of 40 km/h and the other going south at 60 km/h, as shown in the diagram at right. Find the rate at which they are separating after a) 1 h of travel b) 2 h of travel. You must show how to find the answer using calculus. (DIAGRAM IS ATTACHED)

a² +b² = c²
40² + 60² = c²
√4̅0̅²̅ ̅+̅ ̅6̅0̅²̅ = c
c = 72.11 km/h

MY TEACHER SAID THIS, SHE TOOK OFF 4 MARKS: "you cannot just use pythagorean theorem, you must take the derivative of the pythagorean theorem function and then find s'(1) to find the rate of separation. You did not show all of your work and it doesn't show your understanding." (-4 marks)

SO NOW I DID IT THIS WAY?

D = √A^2 + B^2

Using A = 40t and B = 60t to represent the distances with respect to time, we get

D(t) = √(40t)^2 + (60t)^2 = √1600t^2 + 3600t^2 = √5200t^2

D't= 10,400t/2√5200t^2 = 5200t/√5200t^2

After 1 hr
D' (1)= 5200(1)/√5200(1)^2 = √5200 = 72.1 km/h

Is This way better? I mean is it this that my teacher wants me to do? SO that means to get the answer for b (2 hrs), DO I SUB IN THE 2 in the very last step?
 

Attachments

  • sdfsdfsdfs.JPG
    sdfsdfsdfs.JPG
    10.2 KB · Views: 703
Physics news on Phys.org
  • #2
Yes the second way is better. Why not simplify it more:$$
D'(t) = \frac{5200t}{\sqrt{5200t^2}}=\sqrt{5200}$$This tells you that the rate at which they are separating doesn't depend on ##t## so you get the same answer when ##t=2##.

You just got lucky getting the correct answer the first way. That "method" is completely incorrect. Not to mention that the problem instructions said you must use calculus for your method.
 

Related to Please Can someone check my answer, ITS DONE, needs checking.

1. What is the purpose of having someone check my answer?

The purpose of having someone check your answer is to ensure that it is correct and free of errors. By having someone else review your work, you may catch any mistakes or areas that need improvement.

2. How do I know if my answer needs to be checked?

If you are unsure about the accuracy or completeness of your answer, it is always a good idea to have someone else check it. This is especially important for important assignments or projects.

3. Can I trust someone else to check my answer?

Yes, you can trust someone else to check your answer. It is important to choose someone who is knowledgeable and experienced in the subject matter to ensure the accuracy of their review.

4. What should I do if the person checking my answer finds mistakes?

If the person checking your answer finds mistakes, you should carefully review their feedback and make the necessary corrections. It is also helpful to ask for clarification on any areas that may be unclear.

5. Is it necessary to have someone check my answer every time?

It is not necessary to have someone check your answer every time, but it is always a good idea to get a second opinion on important assignments or when you are unsure about the accuracy of your work. This can help improve the quality of your work and catch any mistakes that you may have missed.

Similar threads

  • Calculus and Beyond Homework Help
Replies
2
Views
973
Replies
12
Views
2K
  • Calculus and Beyond Homework Help
Replies
1
Views
1K
  • Calculus and Beyond Homework Help
Replies
12
Views
2K
  • General Math
Replies
14
Views
648
  • Calculus and Beyond Homework Help
Replies
14
Views
2K
  • Introductory Physics Homework Help
Replies
15
Views
231
  • Introductory Physics Homework Help
Replies
20
Views
445
  • Calculus and Beyond Homework Help
Replies
4
Views
4K
Replies
5
Views
3K
Back
Top