A ball is thrown straight upward and rises to a maximum height of 18.0 m
above its launch point. at what height above its launch point has the
speed of the ball decreased to one-half of its initial value?
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kinematic equation
v^2=u^2-2as; v0=,s=18,a=-10m/s/s
u=root 360
(u/2)^2=u^2-2as
=>s=13.5m
