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!

Instantaneous and average velocity help

  1. Sep 21, 2008 #1
    vAn objects moves horizontally according to the following equation s(t)=t3-2t2-5t+6. Determine the instantaneous velocity of the object at t0=1 second using the definition of a derivative at a point.

    v'(t)= lim (s(t0+h)-s(t0))/h
    h-->0


    And
    What is the average velocity of the object from t=0 to t=2?
    Average velocity= (s(t2)-s(t1))/(t2-t1)



    For the first one, i got:
    ((1+h)3-2(1+h)2-5(1+h)+6-13-2(1)2-5(1)+6)/h

    I expanded and factored all of that ang got (h(-1+h+h2)/h then i plugged in 0 for h and got -1 as the instantaneous velocity... is that correct?

    I got the first one... i just added the values wrong... i got -6. But i still dont know how to do the second one.

    and for the second one, i have (3(2)2-4(2)-5)/2-0 but that makes it 0/2 and i know that this cant be.

    Can you please help me?thank you!
     
    Last edited: Sep 21, 2008
  2. jcsd
  3. Sep 21, 2008 #2
    For the second part, it looks like you used the derivative of s (i.e. the velocity) in the numerator. You should use s itself (i.e. plug t1 and t2 into s(t) for the numerator) as in the definition of average velocity.
     
  4. Sep 21, 2008 #3
    so it should just be (-4-0)/(2-0)=-1/2?
     
  5. Sep 21, 2008 #4
    I think so. No. Wait a minute. Check it again. I think your t1 part is wrong. Just check it over carefully.
     
  6. Sep 21, 2008 #5
    wait wouldnt it be -5 for the average velocity instead?
     
  7. Sep 21, 2008 #6
    Yeah. That's what I get.
     
  8. Sep 21, 2008 #7
    thank you!!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Instantaneous and average velocity help
  1. Instantaneous Velocity (Replies: 3)

Loading...