Friction force applied at an unknown angle to horrizontal plane

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Discussion Overview

The discussion revolves around a physics homework problem involving a body being pulled on a horizontal plane with friction. The participants are trying to determine the angle at which a force is applied, given the weight of the body, the coefficient of friction, and the applied force.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents a problem involving a 51 kg body being pulled with a force of 300 N at an unknown angle, seeking help to find that angle.
  • Another participant suggests setting up a free body diagram (FBD) to analyze the forces acting on the body, including the upward component of the applied force and the normal reaction force.
  • A participant expresses difficulty in deriving two equations from the FBD, one involving sine and the other cosine functions.
  • Equations are shared, indicating the balance of forces in both vertical and horizontal directions, leading to a combined equation involving sine and cosine terms.
  • One participant proposes squaring both sides of the equation to express cosine in terms of sine, leading to a quadratic equation in sine, but reports obtaining values outside the valid range for the sine function.
  • This participant questions the validity of the problem statement or suggests there may be missing information due to the lack of real-valued solutions for the angle.

Areas of Agreement / Disagreement

Participants generally agree on the approach of using a free body diagram and setting up equations based on force balances. However, there is disagreement regarding the validity of the problem statement, as one participant finds no real solutions for the angle, suggesting a potential issue with the problem itself.

Contextual Notes

The discussion highlights limitations in the problem setup, including potential missing information or assumptions that may affect the solvability of the equations derived from the FBD.

nialltm1991
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Homework Statement


im having problems with this question...a body weighing 51kg is pulled on a horrizontal plane with coefficient of friction 0.3. a force of 300N is applied at angle x ... find the angle x?


Homework Equations





The Attempt at a Solution


the only solution i have come to is ... cosx + sinx = 0.5 but i can't solve it anymore ... can someone help me please?
 
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can you set up free body diagram...let F=300N , F is applied at angle x, so there is one upward component and one forward component...also normal reaction from the ground is acting upward on body and gravitational force mg is acting downwards...set up FBD with this info and use the fact the fact that net force in both vertical and horizontal directions is zero
 
yes i can i have a fbd ... but then i will have 2 equations with sin in one and cos in the other and that is the part i get stuck at
 
can you write your equations here so i can check them
 
forces up = forces down forces left = forces right
Rn + 300sin(theta) = mg F = 300cos(theta)
Rn + 300sin(theta) = 500.31 muRn = 300cos(theta) because F = muRn
Rn = 300cos(theta)/mu

300cos(theta)/0.3 + 300sin(theta) = 500.31


and that's as far as i can go
 
what you can do is square both sides and then express [tex]\cos^2(x)[/tex] in terms of
[tex]\sin^2(x)[/tex] and then you have a quadratic equation in [tex]\sin(x)[/tex]
letting [tex]y=\sin(x)[/tex], solve the quadratic equation. but i did that and the values
of y i got are -1.66 and 1.935 . since sine function takes values between -1 and 1 , there is no real valued solution for the x. so please solve the quadratic equation on your own and confirm my calculations...if you are getting the same thing , then the problem is either stated incorrectly or there is some missing information.
 

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