Physics Help Forum Rock falls in water

 Energy and Work Energy and Work Physics Help Forum

 Jul 12th 2017, 03:12 AM #1 Junior Member   Join Date: Jul 2017 Posts: 8 Rock falls in water A rock of mass $\displaystyle m$ is at a high $\displaystyle h$ at rest. Under this height there is a container of water of mass $\displaystyle M$, deep $\displaystyle d$. The rock, the water, the air have the same temperature (condition 1). Find the variations of internal energy, the heats and the works transferred in the system rock+water from the condition 1 to the other conditions: Condition 2: the rocks is going in the water (shortly before) Condition 3: the rock has just stopped at the bottom of the container Condition 4: the rock, the water, the air returned to the initial temperature. The friction between rock and air is negligible. How can I deal with this problem?
Jul 12th 2017, 05:28 AM   #2
Senior Member

Join Date: Aug 2010
Posts: 404
 Originally Posted by Berker A rock of mass $\displaystyle m$ is at a high $\displaystyle h$ at rest. Under this height there is a container of water of mass $\displaystyle M$, deep $\displaystyle d$. The rock, the water, the air have the same temperature (condition 1). Find the variations of internal energy, the heats and the works transferred in the system rock+water from the condition 1 to the other conditions: Condition 2: the rocks is going in the water (shortly before) Condition 3: the rock has just stopped at the bottom of the container Condition 4: the rock, the water, the air returned to the initial temperature. The friction between rock and air is negligible. How can I deal with this problem?
Well, what do you know? Before the rock is dropped, condtion 1, it has potential energy relative to the ground. What is that potential energy? In condition 2, shortly before the rock hits the water, the rock has less potential energy. What is its potential energy now? Of course, that lost potential energy has converted to kinetic energy. What is its kinetic energy? When the rock has stopped at the bottom of the container, it has 0 kinetic and potential energy. By the 'conservation of energy' that must have gone somewhere. Where did it go? Find the temperature of rock and water from that.

Last edited by HallsofIvy; Jul 15th 2017 at 09:24 AM.

 Tags falls, rock, water

 Thread Tools Display Modes Linear Mode

 Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post jordanhuh Kinematics and Dynamics 1 Feb 3rd 2014 08:40 AM LittleWing Kinematics and Dynamics 9 Feb 23rd 2011 08:19 AM ndnkobra Kinematics and Dynamics 4 Aug 31st 2009 03:20 AM ob123 Kinematics and Dynamics 1 Jun 8th 2009 06:05 PM John1506 Thermodynamics and Fluid Mechanics 0 Nov 11th 2008 01:47 PM