Water falling into bucket, Force question

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Homework Help Overview

The problem involves water falling into a bucket and calculating the force exerted on a scale after a certain time. The subject area includes concepts of fluid dynamics, force, and momentum in the context of physics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the calculation of the weight of the water and bucket, questioning the additional force needed to account for the momentum of the flowing water. Some express confusion about the relevance of the distance provided and its implications for speed and momentum calculations.

Discussion Status

Some participants have provided calculations and insights regarding the momentum of the water and its impact on the force measured by the scale. There is ongoing exploration of the relationship between distance, speed, and time, with multiple interpretations of the problem being discussed.

Contextual Notes

Participants note that the time given may not correspond to the time it takes for the water to fall from the specified height, and they highlight that the speed of the water is not constant during its fall.

Leeoku
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Homework Statement


13. Water falls at the rate of 271 g/s from a height of 56.2 m into a 776g bucket on a scale (without splashing). If the bucket is originally empty, what does the scale read after 3.14 s?
Answer: 2.50e+01 N



Homework Equations


Density, estimate 1kg/m^3
F = ma (a = gravity)
1kg = 1L


The Attempt at a Solution


In 3 seconds, .271*3 = .851 L dropped->.851 KG
Add weight of bucket, .851+.776 = 1.63 kg
F =ma
= 15.9 N
 
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You found the weight of the water + bucket. Good! But an additional force is required to stop the momentum of the flowing water.
 
i actually have no clue. what I am puzzled at is why they gave us distance. the first thing that comes to mind is work, but i don't think that helps..
 
Leeoku said:
i actually have no clue. what I am puzzled at is why they gave us distance. the first thing that comes to mind is work, but i don't think that helps..
They gave you the distance so you can figure out the speed of the water as it hits the bucket. Hint: Use that speed to find the rate of change of the momentum of the water as it hits the bucket.
 
ok using v=d/t, 56.2/3.14 = 17.9 m/s
Impulse = delta p = (sum F)delta T
Delta p = 15.9*3.14
= 50 N.s
Using 50 as momentum, p = mv
50 = 17.89 M
m = 2.8 kg

Weird part is answer is given in Newtons, so mass*g = 27.4 N. Still not right, close though..
 
Leeoku said:
ok using v=d/t, 56.2/3.14 = 17.9 m/s
Two problems:
(1) The 3.14 s time given is not the time it takes for the water to fall from the given height.
(2) The speed of the water is not constant as it falls.

To find the speed of the water as it hits the scale, treat it as a falling body (falling from rest through a height of 56.2 m).
 

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