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Homework Help: Finding distance using force, acceleration, time

  1. Oct 1, 2008 #1
    A dockworker applies a constant horizontal force of 89.0N to a block of ice on a smooth horizontal floor. The frictional force is negligible. The block starts from rest and moves a distance 12.5m in a time 5.10s .
    A)What is the mass of the block of ice?
    B)If the worker stops pushing at the end of 5.10s , how far does the block move in the next 5.30s ?

    2. Relevant equations: F=ma

    3. The attempt at a solution: well i was able to solve part A by using the equation
    deltaD=(v1+v2)/deltaT to find v2. and then i used a=(v2-v1)/deltaT and plugged it into F=ma to find the mass.
    For part B, i tried using the same equation for finding distance, however it could not be done cause i do not know how to find v2, and if i plug in 0 as v2, i get a wrong answer.

    so basically i need help in solving part B of this problem. thanks.
    Last edited: Oct 1, 2008
  2. jcsd
  3. Oct 1, 2008 #2


    User Avatar
    Homework Helper

    Welcome to PF.

    Don't you want to consider the relationship between x, a, and t?

    x= 1/ 2 * a * t2

    If you find a, then F = ma gives you the mass as I think you already know.

    Part b can be determined by finding the V from

    V2 = 2*a*x

    That times t gives you distance.
  4. Oct 1, 2008 #3
    you mean V^2=2 x .96 x 12.5? that gives me V=4.9, which i already had to use for part A. and if i do 4.9 x 0.2s. i get .98m, which is not the right distance
  5. Oct 1, 2008 #4
    oh wait nvm, i was reading the question wrong, i thought it was asking what the distance was after 5.3 seconds from 5.1 seconds. i didnt know it meant it was asking the distance after 5.3 MORE seconds. thanks, i got the right answer now.
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