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

[mutineer123]

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??

 

[ehild]

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

ehild

 

[azizlwl]

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

Workout separately and added them.

 

[mutineer123]

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!

 

[azizlwl]

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]

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

 

[Emilyjoint]

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