hi,

A pool of 50 m3 at a height of 100 m from a channel is 40 min. How many KW should the pump power be in order to fill it?

how do we calculate?

Best regards

 

How much work will be done? Start with that and show your work.

 

How much work will be done? Start with that and show your work.

50000*10*100=50*10^6

 

50000*10*100=50*10^6

That's just three numbers multiplied together yielding yet a fourth number.

If that's supposed to be an energy, do we just guess what the units are? foot-lbs? ergs? calories? joules?

 

That's just three numbers multiplied together yielding yet a fourth number.

If that's supposed to be an energy, do we just guess what the units are? foot-lbs? ergs? calories? joules?

Yes, JOULE.

 

what should i do next?

 

You need to learn to track your units properly throughout your work. Your first equation should have been something like:

W = mgh
W = Vρgh
W = (50 m^3)(1000 kg/m^3)(9.81 N/kg)(100 m)
W = (49.1 x 10^6 Nm)(1 MJ / 10^6 Nm)
W = 49.1 MJ

What is the definition of power?

 

You need to learn to track your units properly throughout your work. Your first equation should have been something like:

W = mgh
W = Vρgh
W = (50 m^3)(1000 kg/m^3)(9.81 N/kg)(100 m)
W = (49.1 x 10^6 Nm)(1 MJ / 10^6 Nm)
W = 49.1 MJ

What is the definition of power?

P = work / time (W ⁄ t)

 

P = work / time (W ⁄ t)

And, so.....?

 

And, so.....?

In physics, power is the amount of energy transferred or converted per unit time.

 

In physics, power is the amount of energy transferred or converted per unit time.

And so....?

How does that relate to a problem in which you have a certain (and now known) amount of work done in a certain (and given) amount of time?

 

49.1*10^6/60*40=20.41kw ??

 

49.1*10^6/60*40=20.41kw ??

You've been shown an example of how to properly track your units. I'm not even going to look at work that just tacks some desired unit onto a number at the end.

Also, pay attention to proper order of operations.

 

You've been shown an example of how to properly track your units. I'm not even going to look at work that just tacks some desired unit onto a number at the end.

Also, pay attention to proper order of operations.

49.1 x 10^6 Nm / 60 minute*40 minute=20.4KW

 

You've been shown an example of how to properly track your units. I'm not even going to look at work that just tacks some desired unit onto a number at the end.

Also, pay attention to proper order of operations.

I did not understand what you want from me. Please help.

 

49.1 x 10^6 Nm / 60 minute*40 minute=20.4KW

That has two problems with it. First, order of operations means that this evaluates as:

(49.1 x 10^6 Nm / 60 minute) * 40 minute = 32.7 Nm

Second, even if we fix the order of operations you are still dividing Nm (energy) by min² (time-squared), which does not yield units of power. That reveals that you aren't tracking your units, you are merely going through the motions and tacking onto the end the units you would like the answer to have.

You need to get in the habit of USING the units to your advantage -- that means tracking them through each step and ensuring that the units in one step actually match the units from the prior step. We all make silly mistakes and we always will. Most of those mistakes will mess up the units. If we get in the habit of ALWAYS tracking our units, we are virtually guaranteed of catching those mistakes almost immediately.

 

That has two problems with it. First, order of operations means that this evaluates as:

(49.1 x 10^6 Nm / 60 minute) * 40 minute = 32.7 Nm

Second, even if we fix the order of operations you are still dividing Nm (energy) by min² (time-squared), which does not yield units of power. That reveals that you aren't tracking your units, you are merely going through the motions and tacking onto the end the units you would like the answer to have.

You need to get in the habit of USING the units to your advantage -- that means tracking them through each step and ensuring that the units in one step actually match the units from the prior step. We all make silly mistakes and we always will. Most of those mistakes will mess up the units. If we get in the habit of ALWAYS tracking our units, we are virtually guaranteed of catching those mistakes almost immediately.

I understood properly now. Thanks.

 

That has two problems with it. First, order of operations means that this evaluates as:

(49.1 x 10^6 Nm / 60 minute) * 40 minute = 32.7 Nm

Second, even if we fix the order of operations you are still dividing Nm (energy) by min² (time-squared), which does not yield units of power. That reveals that you aren't tracking your units, you are merely going through the motions and tacking onto the end the units you would like the answer to have.

You need to get in the habit of USING the units to your advantage -- that means tracking them through each step and ensuring that the units in one step actually match the units from the prior step. We all make silly mistakes and we always will. Most of those mistakes will mess up the units. If we get in the habit of ALWAYS tracking our units, we are virtually guaranteed of catching those mistakes almost immediately.

Could there be an error in your solution?

 

What do you mean an error in my solution. I never provided a solution. In the text you quoted I merely evaluated YOUR equation according to the rules of precedence in which multiplication and division have the same precedence and are left-associative. Note that doing so messes up the units since it results in units of energy, not power, which is a big red flag indicating that something is wrong.