Calculating Work & Final Velocity of a 70kg Mass

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Homework Help Overview

The problem involves calculating the total work done on a 70kg mass and determining its final velocity after being pushed in different directions. The context is rooted in mechanics, specifically focusing on work and energy principles.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of work done using forces applied over distances and question how to derive the final velocity from the work-energy principle. There is also a focus on the correct application of initial and final kinetic energy in the context of work done.

Discussion Status

Some participants have provided calculations for work done and are exploring the relationship between initial kinetic energy and work to find the final kinetic energy. There is an ongoing clarification regarding the correct formulation of the work-energy equation and the inclusion of initial kinetic energy.

Contextual Notes

Participants are navigating potential misunderstandings regarding the signs of work done and the proper setup of the energy equations. There is an emphasis on ensuring that calculations reflect the physical scenario accurately.

magma_saber
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Homework Statement


A 70kg mass is in a space and moving at 2.5 m/s. You push it with 200N for 4 m. You then move to the front of the mass and push it backwards with 170N for 3 m.

What was the total work done?
What was the final velocity?


Homework Equations


W = rest energy + F1*r - F2*r


The Attempt at a Solution


rest energy = 1/2*70*(2.5)2 = 218.75
F1*r = 200*4 = 800
F2*r = 170*3 = 510
W = 218.75 + 800 - 510 = 508.75 J

How would i get the final velocity?
 
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magma_saber said:
How would i get the final velocity?

Initial KE + Work = Final KE

Initial ½mv² + W = Final ½mv²
 
so its 218.75 + 800 + 510?
 
magma_saber said:
so its 218.75 + 800 + 510?

Perhaps I should rephrase that since you want to plug in numbers literally without thinking about the signs:

Initial ½mv² + ΔW = Final ½mv²

Btw your initial calculation incorrectly includes the initial KE in the ΔW they asked you to find.
 

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