Comments on: Using conservation of energy determine the speed of the 3kg mass as the 5kg mass hits the ground? http://www.energy--talk.com/alternative-energy/using-conservation-of-energy-determine-the-speed-of-the-3kg-mass-as-the-5kg-mass-hits-the-ground/163/ How Can We Be More Energy Efficient? Thu, 09 Feb 2012 00:55:53 +0000 http://wordpress.org/?v=2.6.5 By: David Zukertort Rudel http://www.energy--talk.com/alternative-energy/using-conservation-of-energy-determine-the-speed-of-the-3kg-mass-as-the-5kg-mass-hits-the-ground/163/#comment-293 David Zukertort Rudel Tue, 05 Feb 2008 05:10:55 +0000 http://www.energy--talk.com/alternative-energy/using-conservation-of-energy-determine-the-speed-of-the-3kg-mass-as-the-5kg-mass-hits-the-ground/163/#comment-293 At the start: 5kg mass has 0 kinetic energy and 5*4*9.8 = 196 joules of potential energy. 3kg mass has 0 kinetic energy and 0 potential energy. Total energy = 196 J. At end: 5kg mass and 3kg mass are both moving with some velocity v. 5kg mass has 1/2*5*v^2 kinetic energy and 0 potential energy 3kg mass has 1/2*3*v^2 kinetic energy and 3*9.8*4 = 117.6 Joules of potential energy. Total energy = 4v^2 + 117.6 J. Set this equal to the energy before and solve for v. At the start:

5kg mass has 0 kinetic energy and 5*4*9.8 = 196 joules of potential energy.

3kg mass has 0 kinetic energy and 0 potential energy.

Total energy = 196 J.

At end:

5kg mass and 3kg mass are both moving with some velocity v.

5kg mass has 1/2*5*v^2 kinetic energy and 0 potential energy

3kg mass has 1/2*3*v^2 kinetic energy and 3*9.8*4 = 117.6 Joules of potential energy.

Total energy = 4v^2 + 117.6 J.

Set this equal to the energy before and solve for v.

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