# at what speed was the ???????????

A ball is thrown vertically upwards into the air. It rises a vertical distance of 2.7 m before falling to the ground. Assuming that all of the ball's initial kinetic energy is converted into gravitational potential energy as the ball rises, at what speed was the ball thrown into the air? You should assume g = 9.8 m s�2 and give your answer to an appropriate number of significant figures and in the correct SI units. speed = ???
23:13 Sat 30th May 2009

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 Homework this late...............and on a Saturday !?! 23:15 Sat 30th May 2009 when it's time to answer this question on an exam, will you be able to send a question to the answerbank or will you have to know how to do it yourself? 23:16 Sat 30th May 2009 Speed on leaving the hand is the same as the speed before hitting the ground. You know the acceleration and vertical displacement so apply the appropriate SUVAT equation. 23:32 Sat 30th May 2009 23 feet per second per second 23:35 Sat 30th May 2009 Using v�-u�= 2as: s= 2.7 m v= 0 a=-9.8 m/s� SQRT(2*9.8*2.7) So u= SQRT(2*9.8*2.7) =7.274613392 m/s= 7.3m/s 2 sf) 00:47 Sun 31st May 2009 You should argue it by using the clue in the question, which says that all the ball's kinetic energy is converted to potential energy and write: Kinetic Energy=(1/2)mv^2=mgh(potential energy) So v^2=2gh and the answer is the same as the last poster's 7.3 m/sec taking g=9.8 m/s^2 09:41 Sun 31st May 2009 this section should be renamed "homework i can't be bothered to do" thats all that seems to get posted here recently 12:57 Sun 31st May 2009 I agree. We shouldn't really be doing people's homework for them as they don't learn anything from it. 17:54 Sun 31st May 2009

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