posted by Heaven

An object on Earth falls with an acceleration of a=9.81 m/s^2. A function exists between the height from which the object falls, the initial velocity of the object and the time the object spends in the air. h(t)= Vt + at^2 V=initial velocity. T= time. A= acceleration due to gravity.
A.) Lucy and Kim determine the height of a building by dropping a brick from its roof. The initial velocity will be 0 m/s because Lucy will simply let go of the brick. Kim times the fall of the brick to be 3.5 seconds. What is the height of the building?
B.) Determine the amount of time the brick is in the air if Lucy throws the brick downward with an initial velocity of 5 m/s. Round to the nearest hundredth of a second.

1. Reiny

h(t) - -9.81t^2 + 0t + h = 0 when it hits the ground
when t = 3.5
-9.81(3.5)^2 + h =0
h = 120.1758 m

b) repeat for the equation
h(t) = -9.81t^2 -5t + 120.1725
set that equal to 0
and solve for t , reject any negative values of t

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