Problem with f=ma and E=0.5mv^2

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Discussion Overview

The discussion revolves around the relationship between force, work, and kinetic energy in the context of an object being accelerated. Participants explore the calculations involved in determining the distance traveled by an object under constant acceleration and the implications for kinetic and potential energy. The scope includes conceptual understanding and mathematical reasoning.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant calculates the force on a 1 kg object accelerated at 1 m/s² and attempts to relate work done to kinetic energy.
  • Another participant challenges the distance calculation, asserting that it is not 55 m and prompts a re-evaluation of the method used.
  • A subsequent post provides a detailed breakdown of the distance traveled over time, indicating that the distance is calculated using the formula for distance under constant acceleration.
  • Another participant corrects the original poster's distance calculation, suggesting the use of the formula d = 0.5 * a * t² for constant acceleration.
  • The original poster acknowledges the correction and expresses gratitude, indicating a realization of the need for a different approach to calculating distance.
  • One participant requests further elaboration on the distance calculation method used by the original poster.
  • The original poster reflects on the need for integrals to calculate distance but notes a lack of familiarity with that method.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial calculations presented by the original poster, as there are multiple corrections and clarifications regarding the distance traveled and the formulas used. The discussion remains unresolved regarding the initial misunderstanding of the relationship between work and kinetic energy.

Contextual Notes

The discussion highlights limitations in the original poster's understanding of the equations of motion under constant acceleration and the implications for energy calculations. There is a dependence on the correct application of formulas and assumptions about constant acceleration.

Nal
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EDIT: The question has been answered, and I don't need help anymore. Thanks a lot everybody!

Hi. This is something that has been puzzling me for a while, probably just due to my own stupidity. It seems to me that this should be really simple, but I don't know what I'm doing wrong though, so now I'm putting it out here.

Imagine an object with a mass of 1 kg being accelerated at a rate of 1 m/s^2 over 10 seconds.
We can then calculate the force being applied to the object
F=1*1=1 N

We can also calculate how far the object has moved over these 10 seconds
qovlur.jpg


According to Wikipedia, the work (W) is the product of a force times the distance through which is acts, measured in Joules, so
W=F*d=m*a*d=55 J

The velocity v at which the object moves is t*a=10 m/s
Then we can calculate the kinetic energy E

E=0.5*m*v^2=50 J

But shouldn't E and W be the same?
For example, if we take the object, now with the kinetic energy E and make it go up a hill on a planet where the gravitational acceleration is 1 1m/s^2 (which is =a from before, of course) we will convert the kinetic energy to potential energy, and we can calculate how far up the hill the object will go, as E(kin)+E(pot) is constant

0.5*m*v^2=m*a*h
0.5*1*10^2=1*1*h
h=50 m

But shouldn't h be 55 metres, as that was the distance the object moved when we accelerated it?
I hope you understood what I meant, I'm absolutely horrible at explaining my thoughts.
Thanks in advance! :)
 
Last edited:
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The distance traveled is not 55m.
Check your calculation
 
technician said:
The distance traveled is not 55m.
Check your calculation

Distance traveled over time

after 1s: 1 m (velocity 1 m/s)
2s: 3 m (velocity 2 m/s)
3s: 6 m (velocity 3 m/s)
4s: 10 m (velocity 4 m/s)
5s: 15 m (velocity 5 m/s)
6s: 21 m (velocity 6 m/s)
7s: 28 m (velocity 7 m/s)
8s: 36 m (velocity 8 m/s)
9s: 45 m (velocity 9 m/s)
10s: 55 m (velocity 10 m/s)
 
Your calculations are incorrect. Given a constant acceleration a, distance d as a function of time is given by [itex]d=\frac 1 2 a t^2[/itex].
 
Ah, well that obviously solves it. Thanks a lot.
 
Nal said:
We can also calculate how far the object has moved over these 10 seconds
qovlur.jpg

[/QUOTE

Can you elaborate more on the method you use in finding the distance?
 
azizlwl said:
Nal said:
We can also calculate how far the object has moved over these 10 seconds
qovlur.jpg

[/QUOTE

Can you elaborate more on the method you use in finding the distance?

I should update the main post. I realize now that I should have used integrals to calculate the distance travelled, however I've never learned about any of that. My question has already been answered. Thanks for taking your time to reply, though!
 

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