Solving Question 14: I HAVE NO IDEA WHY MY ANSWER IS WRONG!

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Homework Help Overview

The discussion revolves around a physics problem related to work done against friction and gravitational potential energy. Participants are analyzing a scenario involving forces acting along a slope and the corresponding work calculations.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to understand the discrepancy between their calculated work done and the expected answer. There are discussions about the forces acting on the slope, including friction and gravitational potential energy, and whether to use height or slope distance in calculations.

Discussion Status

Some participants have provided insights into the components of forces and the nature of work done, suggesting that multiple interpretations of the problem are being explored. There is an ongoing examination of the relationship between work done and gravitational potential energy, with no explicit consensus reached.

Contextual Notes

Participants are grappling with the definitions and relationships between work done, friction, and potential energy, indicating a need for clarity on these concepts. The original poster expresses significant concern about their understanding of the material.

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Homework Statement



http://www.xtremepapers.com/CIE/International%20A%20And%20AS%20Level/9702%20-%20Physics/9702_w10_qp_12.pdf

question 14



Homework Equations


mgh=gpE
fxd=workdone



The Attempt at a Solution



I HAVE NO IDEA WHY MY ANSWER IS WRONG! AND THIS IS GETTING ME so WORRIED ABOUT MY CONCEPTUAL UNDERSTANDING!
I found the component down the surface which was 100N, I added 150N to this(as he has to overcome the friction) so now i just use Fxd=250x1.5=375j. But the actual answer is 750j HOW COME??
 
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The 250 N force acts along the length of the slope. 1.5 m is the height.

ehild
 


2 works done here.
1. Overheating the surface, friction.
2. Increases the PE,

Workout separately and added them.
 


ehild said:
The 250 N force acts along the length of the slope. 1.5 m is the height.

ehild
ISn't the energy we are evaluating mgh?(which is the same as Fxd). SO whenever we use gravitational potential energy, shouldn't we use the height and not the slope!
 


mutineer123 said:
I HAVE NO IDEA WHY MY ANSWER IS WRONG! AND THIS IS GETTING ME so WORRIED ABOUT MY CONCEPTUAL UNDERSTANDING!
I found the component down the surface which was 100N, I added 150N to this(as he has to overcome the friction) so now i just use Fxd=250x1.5=375j. But the actual answer is 750j HOW COME??

Since you have found the component down the surface then use the component of length of the surface.

Actually work done= FxdxCosθ
 


mutineer123 said:
ISn't the energy we are evaluating mgh?(which is the same as Fxd). SO whenever we use gravitational potential energy, shouldn't we use the height and not the slope!

The question reads: "What is the work done by the person?".It is not equal to the gravitational potential energy.

ehild
 


the persion pushes along the slope. If you know the height you can calculate the sloping distance.
I also got the total pushing force to be 250N
 

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