An object is dropped from a platform 400 ft high. ignoring wind resistance, what will its speed be when it reaches the ground?

To answer this item, we first convert the given height in meters.
   
  height = (400 ft) x (1 m/ 3.28 ft) = 121.95 m

Then, use the equation of motion which relates the distance covered with the initial and final velocities and the acceleration which takes a form,

   2ad = Vf² - Vi²

Substituting the known values from the given,
  2(9.8 m/s²)(121.95 m) = Vf² - 0²

The value of Vf from the equation is 48.89 m/s. 

If we are to convert this back to feet.
   
  speed = (48.89 m/s)(3.28 ft/1 m) = 160.35 ft/s

160.35 ft/s