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!

Kinematics and also an energy

  1. Dec 17, 2011 #1
    1. The problem statement, all variables and given/known data
    1.A block is sent up a frictionless ramp along which an x axis extends upward. The figure below gives the kinetic energy of the block as a function of position x; the scale of the figure's vertical axis is set by Ks = 38.0 J. If the block's initial speed is 4.70 m/s, what is the normal force on the block?

    2. A startled armadillo leaps upward rising 0.553 m in the first 0.197 s.
    (a) What is its initial speed as it leaves the ground?
    Correct: Your answer is correct. m/s

    (b) What is its speed at the height of 0.553 m?
    Correct: Your answer is correct. m/s

    (c) How much higher does it go?



    2. Relevant equations
    F=ma
    v^2=v0^2+2ad



    3. The attempt at a solution

    For the first question

    KE=.5mv^2
    152 J = .5m(4.70 m/s)^2
    m=13.8 kg

    Height of the ramp
    .5mv^2=mgh
    152 J=13.8kg*9.8m/s^2*h
    h=1.13 m
    Solve for the angle of the ramp
    sin-1(1.13m/2m) = 34 deg
    N-mgcos34=0
    N=13.8*9.8cos34=111 N. But this is wrong.

    2nd question...
    solved pt a and b, got 3.77 m/s for v0, 1.84 m/s vf

    v0 is 0 m/s at the top of the height, so
    0=3.77m/s ^2 +2*9.8m/s^2d
    solve for d, get .725
    difference is .17 m. But this is wrong.

    Thank you so much! Final monday and I have a C-:/
     
  2. jcsd
  3. Dec 17, 2011 #2

    PeterO

    User Avatar
    Homework Helper

    Where did you get 152 Joules from? You said the energy was 38J [which only one quarter of 152]
     
  4. Dec 17, 2011 #3
    Oops! Sorry, forgot to include this image
    http://www.webassign.net/hrw/7-33.gif

    It's a scale of 38 J so, at the top (0m) E=38J(4)=152 J
     
  5. Dec 18, 2011 #4

    PeterO

    User Avatar
    Homework Helper

    Where did you get the idea it is a scale 38J?

    The problem states that Ks = 38J. That is not some sort of scale. They have not said 38J per division.

    Also this problem was the subject of another post earlier?????
     
  6. Dec 18, 2011 #5
    Wow, apparently I can't read.

    And yes, I found that post but I think my setup is different then theirs but still correct.

    I know get a value of 27.9523 N for the normal force.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Kinematics and also an energy
  1. Kinematics and energy (Replies: 2)

Loading...