Friction of an object being pulled up/down

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Homework Help Overview

The discussion revolves around calculating the normal force on an 80 kg object being pulled with a force of 4000 N at angles of 50 degrees and 70 degrees. The context involves understanding the forces acting on the object, particularly in relation to inclined planes and the application of Newton's laws.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the calculation of the normal force using different angles and question the setup of the problem, particularly whether the object is on an inclined plane or a flat surface. There are attempts to apply relevant equations and free body diagrams to clarify the situation.

Discussion Status

The discussion is ongoing, with participants providing different interpretations of the problem setup. Some guidance has been offered regarding the need for free body diagrams and the application of Newton's second law, but there is no explicit consensus on the correct approach yet.

Contextual Notes

There is confusion regarding the scenario being analyzed, specifically whether the object is on an inclined plane or a flat surface, which affects the equations and reasoning used in the calculations.

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Homework Statement


Find the normal force on an object, 80kg, which is being pulled by a force of 4000N. A) Up at an angle of 50 degrees, B) Down at an angle of 70 degrees

Homework Equations


Fn = Fwcosx
Fp = Fwsinx

The Attempt at a Solution



A)
Fp = Fwsinx
Fp = 4000sin50 = 3064N
(80*9.8) - 3064 = -2280N = 2280N

B)
Fp = 4000sin70 = 3758.8N
(80*9.8) + 3758.8 = 4542.7N

Is this correct?
 
Last edited:
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I'm confused. Is the object being pulled up an inclined plane, or is it on a flat surface and the applied force acts at the given angles?
 
Pulled up on an inclined plane.
 
In that case your "Relevant Equations" are wrong. You need to draw a free body diagram and apply Newton's 2nd law to it. That's how you do every inclined plane problem.
 
Tom Mattson said:
In that case your "Relevant Equations" are wrong. You need to draw a free body diagram and apply Newton's 2nd law to it. That's how you do every inclined plane problem.

Ah...I believe I was doing the other scenario then. In that case, I would simply do Fn = 80 * 9.8 * cos 50 = 503.9 N and Fn = 80 * 9.8 * cos70 = 268.14N, correct?
 
Last edited:
The other scenario doesn't make much sense. If you pull on an 80 kg object with 4000 N at 50 degrees, the object will be lifted right off the ground. Hence, no normal force.
 

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