Anonymous asked in Science & MathematicsZoology · 8 months ago

Physics Word Problem Please?

A slingshot fires a pebble from the top of a building at a speed of 14.0 m/s. the building is 31.0 m tall. Ignoring air resistance, find the speed with which the pebble strikes the ground when the pebble is fired a) horizontally, b) vertically straight up, c) vertically straight down.

3 Answers

  • 8 months ago
    Favourite answer

    Have you been taught the conservation of energy?

    Change in potential energy is the same no matter how it gets there.

    Given no change in total mechanical energy,

    v = sqrt(14^2 + 2*9.81*31) m/s

    If not then use kinematics formulas.

    • NCS
      Lv 7
      8 months agoReport

      ... which will of course yield the same results.

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  • 8 months ago

    You have to memorize trajectory equations.

    Vo Horizontal

    Vyf² = 0²+2*g*d = 19.6*31 = 24.65 at impact

    Vxf = 14m/s at impact so 

    Vf² = 24.65²+14² = 28.3m/s at impact a)

    Vo straight up

    Find time of flight 

    31 +14*t - 4.9*t² = 0

    t = 4.32

    Vy(4.32) = 14 - 9.8*4.32 = -28.3m/s (down) at impact b) 

    Vo straight down

    Vyf² = 14²+19.6*31 = 28.3²

    28.3m/s (down) at impact c)

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  • Anonymous
    8 months ago

    a) 28 m/s

    b) 28 m/s

    c) 28 m/s

    Gravity is a conservative field

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