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Old Feb 2nd 2013, 01:14 AM   #1
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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?
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Old Feb 2nd 2013, 07:48 PM   #2
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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.
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Old Feb 2nd 2013, 08:03 PM   #3
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Originally Posted by Agent87 View Post
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.
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Old Feb 3rd 2013, 12:55 AM   #4
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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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