Determine acceleration given work done and vertical distance

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Homework Help Overview

The problem involves determining the acceleration of a mass that is raised vertically, given the work done and the height. The subject area includes concepts from mechanics, specifically work, force, and acceleration.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the incomplete nature of the problem, questioning the specifics of the forces involved and the assumptions that must be made. Some suggest considering the work done by the lifting force versus gravitational force.

Discussion Status

The discussion is ongoing with various interpretations being explored. Some participants have attempted calculations based on different assumptions, while others have pointed out inconsistencies and the need for clarification on the forces acting on the mass.

Contextual Notes

There are indications that assumptions about the nature of the work done and the forces involved may be necessary to progress, as the original problem statement lacks clarity on these points.

kaspis245
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1. A body, whose mass is 10kg, is vertically raised upwards h=2 m . 230J work was done. Find the acceleration.

Homework Equations


W = Fh
F = ma

The Attempt at a Solution


W = Fh

F = A/h = 230J / 2m = 115J

F = ma

a = F/m = 115J/10kg = 11.5 m/s^2
 
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The question is incomplete. The work done on what by what force?

If it is the work done by the lifting force on the mass, the acceleration of the mass is not only dependent on this force.
 
So, what's the solution then?
 
When a problem is (or even appears to be) incompletely specified, you should point that out, make some reasonable assumptions and state those assumptions along with your solution.

For instance you might assume that the work in question is that done by the external lifting force, excluding gravity.
 
You need to solve it with the information given, which means you need to make some assumptions.

It could be useful to turn around the problem and think about what would have been the work done if there were no acceleration. With that clear, it could be easier to see how to solve the original situation.
 
OK, I think now it's correct:

A = Fh

F = A/h = 230J/2m = 115N

F1 - mg = F

F1 = F + mg = 115N + 10kg*10m/s2 = 215 N

F1 = ma

a = F1/m = 215N / 10kg = 21.5 m/s2
 
Well, except that the lifting force and gravity are working in different directions ...
 
Hey, I have found another solution, but the answer is different:

A = Ek = mv2/2

V2 = 2A/m = 46 (m/s)2

V2 = vo2+2as

a = v2/ 2h = 11.5 m/s

So why is that?
 
That solution has the same problem as your original one. It assumes that there is no gravitation.
 

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