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intro to physics

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a toy rocket moving vertically upward passes by a 2.2m- high window whose sill is 7.0m above the ground. the rocket takes 0.17s to travel the 2.2m height of the wondow
part a): what was the launch speed of the rocket ? assume the propellant is burned very quickly at blastoff

part b) how high will the rocket go ?

  • intro to physics - ,

    Let’s find the initial velocity of rocket.
    Since
    h(o) = v(o)•t - g•t^2/2,
    v(o) = 2• h(o) /t +gt/2 = 22.2/0.17 + 9.8•0.17/2 = 25.047 m/s.
    Now let’s find the time of reaching the max height
    0 = v(o) - g•t1
    t1 = v(o)/g = 25.047/9.8 = 2.56 s.
    The max height (from the sill)
    h1 = v(o)•t1-gt1^2/2 = 25.047•2.56 =9.8•(2.56)^2/2 = 96.13 m.
    The max height (from the ground) is
    H = 96.13 + 7 = 103.13 m.
    H = gt2^2/2 .
    t2= sqrt(2•H/g) = sqrt(2•103.13/9.8) = 4.59 s.
    v =g•t2 = 9.8•4.59 = 44.96 m/s

  • intro to physics - ,

    where did that 22.2 come from?

  • intro to physics - ,

    v(o) = 2• h(o) /t +gt/2 = 2.2/0.17 + 9.8•0.17/2 = 25.047 m/s.

  • intro to physics - ,

    22.2 was a typo error of 2*2.2, but the result was ok.

  • intro to physics - ,

    thats wrong, no 2* h(o)

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