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Homework Help: Can someone please solve this physics problem?

  1. Jul 3, 2017 #1
    I won't necessarily understand it unless it's solved so I can go through all the steps, it would be greatly appreciated. It's a practice book work problem.

    Suppose an object of mass 2 slugs is shot vertically upward with an initial velocity of Vo = 200 ft/sec. Assume that air resistance is proportional to instantaneous velocity. Acceleration due to gravity is = 32 ft/sec^2 (with k=0.03)

    a) Find velocity of object at time t

    b) Find the time it takes for the object to reach its max height
  2. jcsd
  3. Jul 3, 2017 #2
    let u = initial velocity g = gravitational acceleration maximum height
    using u^2 / 2g = h, h = 625ft (max height)
    since t = (v1 - v2)/a , t for max height = (200-0)/32 = 6.25s
    If you want to find the velocity for time t, sub your values back in.
    Last edited by a moderator: Jul 3, 2017
  4. Jul 3, 2017 #3
    thank you so much, but can you please show what you mean by "plug in values in"....like I said it's better for me to see step by step, I haven't taken physics in years.
  5. Jul 3, 2017 #4


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    You seem to have calculated u2/g2, not u2/2g.
    And you have ignored air resistance. (I assume k = 0.03 is the proportionality of air resistance to instantaneous velocity.)
    Can you write an equation for the force acting on the object at any instant? What is its acceleration? What is its velocity and height as a function of time?
    OP, you are expected to show some work of your own before receiving help. You have had some hints, what can you make of them?
  6. Jul 3, 2017 #5
    no wonder the height did not make sense to me, i have miscalculated
  7. Jul 3, 2017 #6
    Sorry mjc this is my first time on the forums, can you solve this one for me and I will go on and show work in the future before asking help? This problem has been really bugging me.
  8. Jul 3, 2017 #7


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    Staff: Mentor

    Thread closed for Moderation.
  9. Jul 3, 2017 #8


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    Staff: Mentor

    No, absolutely not. It is against the PF schoolwork rules for any of us to do your homework/schoolwork for you. Please re-read the PF Rules (see INFO at the top of the page), and check your PMs.

    @awpbash and @mjc123 -- It is also against the PF Rules for you to provide help when the poster has shown no effort. They must post using the Homework Help Template and fill out all the sections, including their Attempt at a Solution. Please in the future if you see a post like this with no effort and asking for the solution, click the Report link on the post to let the Mentors know to handle it.

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