Some drops a ball off of the top of a 125-m-tall building. In this prob-lem, you will be solving for the time it takes the ball to hit the ground.(a)Define your coordinate system, be thorough.(b)Write down the given infor-mation, be sure to include hidden information.(c)State what physics principleis at play here. How do you know this?(d)Select an equation.(e)Solve forthe time it takes for the ball to hit the ground.


  1. Answer:

    t = 5.05 s


    This is a kinetic problem.

    a) to solve it we must fix a reference system, let’s use a fixed system on the floor where the height is 0 m

    b) in this system the equations of motion are

                  y = v₀ t + ½ g t²

    where v₀ is the initial velocity that is v₀ = 0 and g is the acceleration of gravity that always points towards the center of the Earth

    e)    y = 0 + ½ g t²

         t = √ (2y / g)

         t = √(2 125 / 9.8)

         t = 5.05 s


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