Search: To find out answers to a specific question, copy a representative sentence from the question and paste the sentence in the search form and search it. The results show the most related questions and yours may be in there. Feel free to share LeiAcademy.org with other teachers and students.  
To discourage spam, only registered users can ask questions.

Welcome to Physics Homework and Study Help, where you can ask questions and receive help on learning physics. We currently focus on helping questions in introductory level college physics and high school AP Physics courses.
To discourage spam, only registered users can ask questions.

Facebook Twitter Google

Welcome to Physics Homework Help Page on LeiAcademy.org

Feel free to ask a question and also answer questions others asked. Answering others' questions can in turn help one's own understanding and build a warm healthy community for learning. The followings list a few things that might be helpful for you to effectively obtain help on specific physics homework or practice problems.  

Search: To find out answers to a specific questions, copy a representative sentence from the question and paste the whole sentence in the search form and search it. The results will show the most related questions and yours may be in there

Browse: To find out what have been discussed, asked or answered, put in a few key words in the search form and search for related questions, answers, and or solutions. Or you can click the related tags or other tabs to find useful information there. 

You can also write professional-looking equations using Latex codes (see details here).

This site is hosted on LeiAcademy.org, which will continue to add new resources for learning. Feel free to share this with other teachers and students.  

For HW 8, problem 12, how can i find what the scale reads at the end of the problem?

0 votes
1,642 views

This is problem 12 in physics 1250. Water falls without splashing at a rate of 0.320 L/s from a height of 2.20 m into a 0.760-kg bucket on a scale. If the bucket is originally empty, what does the scale read 4.00 s after water starts to accumulate in it?

asked Oct 14, 2013 in Intro College Physics by anonymous
recategorized Oct 14, 2013 by LeiBao

1 Answer

0 votes
The scale reads the total force pushing down on it by the bucket which includes two parts:

1) the weight of the water accumulated in the bucket,

2) the average force created by water falling into the bucket and deaccelerating into zero velocity -- here you will have a change of momentum for water: ||\Delta P=F_{ avg }\Delta t||.

The weight of the water in the bucket is easy to find out -- just get the volume and multiple density (1 kg/liter) to get mass.

To find the average force needed to change the water's momentum, first you need to find its velocity right before the water stream hits the bucket. You can get this by using the free-fall of water from a height given in the question: ||V_{ f }^{ 2 }-V_{ i }^{ 2 }=2gh||.

To find ||\Delta P|| of water for some time, you need to find the volume of the water dropped over that time and then the change of the momentum of that amount of water: (note that the water's density is 1kg/liter and define downward being positive)

$$V_{ water }=flowrate\cdot \Delta t \\ \\

M_{ water }=V_{ water }\cdot density=flowrate\cdot density \cdot \Delta t \\ \\

\Delta P=0-flowrate\cdot density\cdot V_{ f }\cdot \Delta t=F_{ avg }\cdot \Delta t\\ \\

F_{ avg }=-flowrate\cdot density\cdot V_{ f }$$

Give it a try and see if it helps.
answered Oct 14, 2013 by LeiBao (360 points)
web counter
...