Posted by Mima on Sunday, September 16, 2012 at 4:52pm.
A soccer ball is kicked from the ground with an initial speed of 14.5 m/s. After 0.272 seconds, ts speed is 12.4 m/s. (A) Give a strategy that will allow you to calculate the ball's initial direction of motion. (B) Use your strategy to find the initial direction.

physics  Elena, Monday, September 17, 2012 at 4:34pm
v₀⒳= v₀•cosα,
v₀⒴ =v₀•sinα,
v₀² =v₀⒳² +v₀⒴²,
v² =v⒳² +v⒴²,
v⒳= v₀⒳,
v⒴=v₀⒴ g•t,
v² =v⒳² +v⒴² = v₀⒳²+(v₀⒴ g•t)²=
=v₀⒳²+v₀⒴² 2 v₀⒴•g•t +(g•t)² =
= v₀²2 v₀•sinα•g•t +(g•t)².
sinα= [v₀²v²+(g•t)²]/2•v₀•g•t =
=[14.5² 12.4²+(9.8•0.272²]/(2•14.5•9.8•0.272) =
=0.823.
α=55.35°
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