• Support PF! Buy your school textbooks, materials and every day products via PF Here!

Boats boats boats

  • Thread starter zapped
  • Start date
12
0
1. Homework Statement
A boat leave a dock at noon and heads weat at a speed 25km/h. Another boat heads north at 20km/h and reaches the same dock at 1:00 pm. when were the boats closest to each other?


2. Homework Equations
when were the boats closest to each other?



3. The Attempt at a Solution
I use the pythagorean for the distance
but I'm not sure about how to sub them in?
I tried to assume that the second boat also leaves at noon, so the total distance will be 20km. But thats wrong. Please help, thanks =P[/b]
 
14
0
d(distance)/dt = 0

Calculate the following quantities in order. All but the last one are functions of time:
  1. the vector position of each boat
  2. the vector distance between the boats
  3. the magnitude of that distance
  4. the time derivative of that magnitude
  5. the time at which that derivative is zero
As long as the distance between the boats varies smoothly in time, its time derivative will be zero when the distance is at a minimum.
 
351
2
At t = 0, the first boat has already traveled 25 km.

So, at any t > 0

dist btw. them ^ 2 = distance covered by boat 2 ^ 2 + (distance by 1 + 25 ) ^ 2

You need to differentiate this equation to get speeds in it.

A diagram about the situation would be a big help.
 

Related Threads for: Boats boats boats

  • Posted
Replies
2
Views
2K
  • Posted
Replies
1
Views
1K
  • Posted
Replies
8
Views
10K
  • Posted
Replies
11
Views
18K
Replies
6
Views
2K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top