Physics Help Forum Object projected vertically upward-Kinetic Energy problem.

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 Feb 2nd 2013, 12:14 AM #1 Junior Member   Join Date: Feb 2013 Posts: 2 Object projected vertically upward-Kinetic Energy problem. Hi all, An object is projected vertically upwards and reaches a maximum height of 250m. Calculate the kinetic energy and velocity when the object is 200m above ground while moving downwards. To Calculate V: Using V= √(2.g.s) = √(2.(9.8).50) = 31,305 m/s But the book gives the answer as 10 m/s, how did they get this answer? What am I doing wrong?
 Feb 2nd 2013, 06:48 PM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,347 Assuming there's no mistake in the data, your answer is correct. An object falling 50 meters attains a speed of sqrt(2gh), which for h=50 meters is about 31.3 m/s.
Feb 2nd 2013, 07:03 PM   #3
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 Originally Posted by Agent87 Hi all, An object is projected vertically upwards and reaches a maximum height of 250m. Calculate the kinetic energy and velocity when the object is 200m above ground while moving downwards. To Calculate V: Using V= √(2.g.s) = √(2.(9.8).50) = 31,305 m/s But the book gives the answer as 10 m/s, how did they get this answer? What am I doing wrong?
Nothing. Book error. They apparently used a rounded off g = 10m/s^2, but then incorrectly used the distance travelled down from 250 to 200 m as 5 m instead of 50 m.

 Feb 2nd 2013, 11:55 PM #4 Junior Member   Join Date: Feb 2013 Posts: 2 Thanks for the help, I wanted to make sure the problem was in the text book and not in my calculations.

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