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A 1 Kg object is dropped from rest from a helicopter at an altitude of 2000 meters?

  1. Dec 14, 2009 #1
    A 1 Kg object is dropped from rest from a helicopter at an altitude
    of 2000 meters. What is the velocity of the object just before it lands upon a thick bed of pillows? The top of the pillow stack is at zero altitude. If the restoring force
    constant (spring constant) of the stack of pillows is 1 N/m, how far into the stack will the
    object travel before it comes to a full stop? Neglect air resistance.
     
  2. jcsd
  3. Dec 14, 2009 #2

    CompuChip

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    Re: A 1 Kg object is dropped from rest from a helicopter at an altitude of 2000 meter

    So you can start by calculating the final velocity. There are two ways to go here: one would be to use forces (Newton's laws, etc); and the other is using energies (conversion from potential to kinetic energy, etc).

    Since the second part of the question includes a spring, I suggest you are supposed to use energies here?

    So there are two relevant points: the point where the object is dropped and the point 2000 meters below it where it hits the pillows. As you know, the total energy
    Etotal = Epotential + Ekinetic
    is conserved (i.e. the same at these two points), where Epotential is the gravitational energy.
    Can you give me the formulas for the two quantities on the right hand side and express them in given values and unknowns?
     
  4. Dec 14, 2009 #3
    Re: A 1 Kg object is dropped from rest from a helicopter at an altitude of 2000 meter

    Would it be

    mgh + 1/2mv2

    (1kg)(9.8m/s2)(2000m) + (1/2)(1kg)(v)2
     
  5. Dec 14, 2009 #4
    Re: A 1 Kg object is dropped from rest from a helicopter at an altitude of 2000 meter

    After you solve for v you get 200 m/s.

    Do you set the KE = to the spring equation after that to find distance it goes into pillows?

    1/2mv^2 = kX?
     
  6. Dec 14, 2009 #5
    Re: A 1 Kg object is dropped from rest from a helicopter at an altitude of 2000 meter

    almost--energy in a spring is of the same form=1/2kx^2 As written above you are equating energy and force.
     
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