1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: A Person in Free Fall Newton's 2nd Law

  1. Oct 15, 2012 #1
    A Person in "Free Fall" Newton's 2nd Law

    1. The problem statement, all variables and given/known data
    An 80kg aviator is in free fall and acquires a velocity of 60 m/s and then opens his parachute.
    After falling an additional 30m, his velocity has been reduced to 20 m/s. What is the average acceleration of the aviator while his fall is being checked? What is the average force being exerted by the parachute?

    2. Relevant equations
    Force = Mass * acceleration
    Average acceleration = change in velocity/change in time

    3. The attempt at a solution
    Any help would be appreciated, Dont understand how to go about problem
  2. jcsd
  3. Oct 15, 2012 #2


    User Avatar
    Science Advisor

    Re: A Person in "Free Fall" Newton's 2nd Law

    If a person has intial speed [itex]v_0[/itex] and constant acceleration [itex]a[/itex] has, after time t, speed [itex]at+ v_0[/itex] and will have gone distance [itex](a/2)t^2+ v_0t[/itex]. So we will fall "an additional 30m" when [itex](a/2)t^2+ 60t= 30[/itex]. Solve the quadratic equation [itex](a/2)t^2+ 60t- 30= 0[itex] for t. Of course, that will depend on a. Put that value of t into [itex]at+ 60= 20[/itex] and solve that equation for a.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook