Physics Help Forum Kinetic and potential energy

 Energy and Work Energy and Work Physics Help Forum

 Mar 18th 2013, 09:28 AM #1 Junior Member   Join Date: Mar 2013 Posts: 5 Kinetic and potential energy I am having some problem understanding this question, A batsman strikes a ball of 500 gm, from 1m above the ground,upwards to a height of 10m and the wicket keeper catches the ball at almost the same point and the same level from the ground. Find: a) Kinetic energy with which the ball strikes the gloves of the keeper. b) Velocity of ball immediately after striking the bat. c) Potential energy of the ball 5m above the ground. d) Net work done against gravity. What i particularly don't understand is "the wicket keeper catches the ball at almost the same point and the same level from the ground." Please help i am really confused.
Mar 18th 2013, 09:51 AM   #2
Member

Join Date: Feb 2013
Location: NM
Posts: 94
 Originally Posted by noddy I am having some problem understanding this question, A batsman strikes a ball of 500 gm, from 1m above the ground,upwards to a height of 10m and the wicket keeper catches the ball at almost the same point and the same level from the ground. Find: a) Kinetic energy with which the ball strikes the gloves of the keeper. b) Velocity of ball immediately after striking the bat. c) Potential energy of the ball 5m above the ground. d) Net work done against gravity. What i particularly don't understand is "the wicket keeper catches the ball at almost the same point and the same level from the ground." Please help i am really confused.
The ball went straight up .. or at least close enough to straight up that the horizontal component of motion can be neglected. The plot of height as a function of time is a parabola, and by symmetry the speed coming back down will be the same as the initial upward speed (final velocity is the negative of the initial). Since the initial and final vertical positions are the same, you can consider the elevation of 1 m to be the zero of the potential energy.
__________________
DrPhil (not the TV guy)
If we knew what we were doing, we wouldn't have to do it.

 Mar 18th 2013, 10:18 AM #3 Junior Member   Join Date: Mar 2013 Posts: 5 Ok, so does that mean, that the wicket keeper caught the ball when it came down to a distance of 1m from the ground ?
Mar 18th 2013, 12:21 PM   #4
Member

Join Date: Feb 2013
Location: NM
Posts: 94
 Originally Posted by noddy Ok, so does that mean, that the wicket keeper caught the ball when it came down to a distance of 1m from the ground ?
Yes. You can assume the point of the catch is the same as the point at which the ball left the bat.
__________________
DrPhil (not the TV guy)
If we knew what we were doing, we wouldn't have to do it.

 Mar 18th 2013, 06:53 PM #5 Junior Member   Join Date: Mar 2013 Posts: 5 Thank you ! got it now .
Jan 3rd 2014, 01:21 PM   #6
Physics Team

Join Date: Apr 2009
Location: Boston's North Shore
Posts: 1,573
 Originally Posted by noddy Thank you ! got it now .

There's only twe things that anybody needs about potential energy. They are

(1) The potential energy function U is defined such that a particle in such a potential experiences a force given by F = -grad U

(2) If the potential function is not a function of time then the sum of kinetic energy and potential energy is a constant of motion.

 Thread Tools Display Modes Linear Mode

 Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post arangu1508 Energy and Work 2 Oct 20th 2015 11:28 AM man_in_motion Periodic and Circular Motion 2 Mar 19th 2010 01:43 AM s3a Energy and Work 4 Jun 17th 2009 12:08 AM s3a Energy and Work 1 May 28th 2009 07:02 PM Joene Energy and Work 5 Mar 26th 2009 05:04 AM