1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finding Velocity and Displacement

  1. Sep 12, 2004 #1
    My problem states: A speedboat starts from rest and accelerates at +2.01 m/s^2 for 7.25s. At the end of this time, the boat continues for an additional 6.05s with an acceleration of +0.518 m/s^2. Following this, the boat accelerates at -1.49 m/s^2 for 8.05s.

    (a) What is the velocity of the boat at t = 21.35s?

    (b) Find the total displacement of the boat.


    So here was my thinking. The boat was speeding up during the first two stages and slowing down during the third. t = 21.35s is nothing more than the three time intervals given in the question added together. So couldn't I just find the velocity for each time interval and then add them together? At least that's what I tried to do, and my answer was incorrect. I was having trouble discerning what the starting velocity would be for the last two intervals as the first one is clearly 0m/s.

    I'm assuming also that once I've found the velocity at t = 21.35s. I will be able to use that to find the total displacement.
     
  2. jcsd
  3. Sep 12, 2004 #2

    Tide

    User Avatar
    Science Advisor
    Homework Helper

    It doesn't work that way. You have to treat each interval separately.
     
  4. Sep 12, 2004 #3
    Right, I suspected that. So even if I found the velocities of each time interval and added them together, that wouldn't give me the velocity of t = 21.35s.?
     
  5. Sep 12, 2004 #4

    Tide

    User Avatar
    Science Advisor
    Homework Helper

    Nope! You're just going to have to do it!
     
  6. Sep 12, 2004 #5
    Do what?! LOL Obviously, I have no idea what I'm doing. So I find the velocities of each interval, then what??
     
  7. Sep 12, 2004 #6

    Tide

    User Avatar
    Science Advisor
    Homework Helper

    Find the velocities AND the distances for each interval. Use the velocity and position for each interval as the starting conditions for the next interval. Then you're done! :-)
     
  8. Sep 12, 2004 #7
    Alright. I liked my initial way of doing things better. LOL
     
  9. Sep 12, 2004 #8

    Tide

    User Avatar
    Science Advisor
    Homework Helper

    Yes, but just think of all fun you'll have on the journey!
     
  10. Sep 12, 2004 #9
    Well I'll admit, it wasn't as bad as I thought it would be.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?