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1 mark question on application of components and workdone(gravitanal potential energy

1. The problem statement, all variables and given/known data

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

question 14



2. Relevant equations
mgh=gpE
fxd=workdone



3. 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??
 

ehild

Homework Helper
15,314
1,739
Re: 1 mark question on application of components and workdone(gravitanal potential en

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

ehild
 
1,065
10
Re: 1 mark question on application of components and workdone(gravitanal potential en

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

Workout separately and added them.
 
Re: 1 mark question on application of components and workdone(gravitanal potential en

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, shouldnt we use the height and not the slope!
 
1,065
10
Re: 1 mark question on application of components and workdone(gravitanal potential en

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
 

ehild

Homework Helper
15,314
1,739
Re: 1 mark question on application of components and workdone(gravitanal potential en

ISn't the energy we are evaluating mgh?(which is the same as Fxd). SO whenever we use gravitational potential energy, shouldnt 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
 
Re: 1 mark question on application of components and workdone(gravitanal potential en

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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