text: # Friction and velocity help
  
  ## Homework Statement
  
  An 85-N box of oranges is being pushed across a horizontal floor. As it moves, it is slowing at a constant rate of 0.90 m/s each second. The push force has a horizontal component of 20 N and a vertical component of 25 N downward.
  
  Basically, f=ma
  
  ## The Attempt at a Solution
  
  Okay, this is what I attempted. I drew a FBD, so the eqn I came up with is
  fk - Fx = 0
  fk = Fx
  fn - w - Fy = 0
  fn = w + Fy
  And since fk = uk(fn)
  Then shouldn't uk = Fx/(w+Fy)?
  
  I know that's wrong because I didn't include the velocity. But I don't know how to integrate the velocity in there. If it's slowing down, that's only because of the friction force right? And at a constant rate just means the acceleration is zero....What other logic am I missing? Many thanks in advance.
  
  Related Introductory Physics Homework Help News on Phys.org
  Doc Al
  Mentor
  What you are given is not a velocity, but an acceleration. It's undergoing a constant acceleration, not constant velocity. The sum of forces in the horizontal (x) direction is not zero, since the box is accelerating.
  
  Hootenanny
  Staff Emeritus
  Gold Member
  Okay firstly, I need to correct your question. Notice the alteration is red
  
  ## Homework Statement
  
  An 85-N box of oranges is being pushed across a horizontal floor. As it moves, it is slowing at a constant rate of 0.90 m/s2 each second. The push force has a horizontal component of 20 N and a vertical component of 25 N downward.
  If the box is slowing then it is undergoing an acceleration, which is the rate of change of velocity wrt time and has units of meters per second per second. I'm going to ignore your working, because I think you have a fundamental misunderstanding here.
  If it's slowing down, that's only because of the friction force right?
  Correct
  And at a constant rate just means the acceleration is zero
  This is simply wrong. If an object is slowing down how can the acceleration possibly be zero? Remember, as I said above that acceleration is the rate of change of velocity. It therefore follows that if the box is slowing down it has a non constant velocity (i.e. its velocity is changing) and hence the acceleration must be non-zero. Do you follow?
  
  EDIT: Dammit Doc
  
  But the unit is m/s, isn't acceleration m/s^2?
  
  Edit: Okay nvm, I got it. Thanks for both the help!
  
  Hootenanny
  Staff Emeritus
  Gold Member
  But the unit is m/s, isn't acceleration m/s^2?
  You're correct, so I assume either you've incorrectly copied the problem or there has been a typo. However, you should have considered this yourself, the question as written is illogical; how can a box be slowing down and yet have a constant velocity?
  
  Last edited:
  Doc Al
  Mentor
  There's no typo and the units given in the problem statement are correct:
  As it moves, it is slowing at a constant rate of 0.90 m/s each second.
  Note that it says 0.90 m/s each second, which is equivalent to 0.90 m/s/s or m/s^2.
  
  (Of course you did leave out part of the problem statement: The question itself! Which I assume is to find the coefficient of friction.)
  
  Hootenanny
  Staff Emeritus
explanation: This document is a physics homework help request and response. It contains a question about the forces acting on a box of oranges being pushed across a horizontal floor, and the user is seeking help to solve the problem. The user provides their attempt at a solution and expresses confusion about how to incorporate the given acceleration into their equations. The response from a mentor corrects the user's misunderstanding about the relationship between velocity and acceleration and guides them towards the correct approach.
distilabel_metadata.content: Evaluate the user given text extract and determine if it contains a math question and optionally and answer to this question.
  
  Output rules:
  
  1. Briefly describe the document and mention if it contains a question or a question and answer.
  2. Finalize the output with: Label: no-question,question,question-and-answer,multiple-question,multiple-question-and-answer
distilabel_metadata.role: system
distilabel_metadata.content: # Friction and velocity help
  
  ## Homework Statement
  
  An 85-N box of oranges is being pushed across a horizontal floor. As it moves, it is slowing at a constant rate of 0.90 m/s each second. The push force has a horizontal component of 20 N and a vertical component of 25 N downward.
  
  Basically, f=ma
  
  ## The Attempt at a Solution
  
  Okay, this is what I attempted. I drew a FBD, so the eqn I came up with is
  fk - Fx = 0
  fk = Fx
  fn - w - Fy = 0
  fn = w + Fy
  And since fk = uk(fn)
  Then shouldn't uk = Fx/(w+Fy)?
  
  I know that's wrong because I didn't include the velocity. But I don't know how to integrate the velocity in there. If it's slowing down, that's only because of the friction force right? And at a constant rate just means the acceleration is zero....What other logic am I missing? Many thanks in advance.
  
  Related Introductory Physics Homework Help News on Phys.org
  Doc Al
  Mentor
  What you are given is not a velocity, but an acceleration. It's undergoing a constant acceleration, not constant velocity. The sum of forces in the horizontal (x) direction is not zero, since the box is accelerating.
  
  Hootenanny
  Staff Emeritus
  Gold Member
  Okay firstly, I need to correct your question. Notice the alteration is red
  
  ## Homework Statement
  
  An 85-N box of oranges is being pushed across a horizontal floor. As it moves, it is slowing at a constant rate of 0.90 m/s2 each second. The push force has a horizontal component of 20 N and a vertical component of 25 N downward.
  If the box is slowing then it is undergoing an acceleration, which is the rate of change of velocity wrt time and has units of meters per second per second. I'm going to ignore your working, because I think you have a fundamental misunderstanding here.
  If it's slowing down, that's only because of the friction force right?
  Correct
  And at a constant rate just means the acceleration is zero
  This is simply wrong. If an object is slowing down how can the acceleration possibly be zero? Remember, as I said above that acceleration is the rate of change of velocity. It therefore follows that if the box is slowing down it has a non constant velocity (i.e. its velocity is changing) and hence the acceleration must be non-zero. Do you follow?
  
  EDIT: Dammit Doc
  
  But the unit is m/s, isn't acceleration m/s^2?
  
  Edit: Okay nvm, I got it. Thanks for both the help!
  
  Hootenanny
  Staff Emeritus
  Gold Member
  But the unit is m/s, isn't acceleration m/s^2?
  You're correct, so I assume either you've incorrectly copied the problem or there has been a typo. However, you should have considered this yourself, the question as written is illogical; how can a box be slowing down and yet have a constant velocity?
  
  Last edited:
  Doc Al
  Mentor
  There's no typo and the units given in the problem statement are correct:
  As it moves, it is slowing at a constant rate of 0.90 m/s each second.
  Note that it says 0.90 m/s each second, which is equivalent to 0.90 m/s/s or m/s^2.
  
  (Of course you did leave out part of the problem statement: The question itself! Which I assume is to find the coefficient of friction.)
  
  Hootenanny
  Staff Emeritus
distilabel_metadata.role: user
distilabel_metadata.raw_output_q_a_detector_0: This document is a physics homework help request and response. It contains a question about the forces acting on a box of oranges being pushed across a horizontal floor, and the user is seeking help to solve the problem. The user provides their attempt at a solution and expresses confusion about how to incorporate the given acceleration into their equations. The response from a mentor corrects the user's misunderstanding about the relationship between velocity and acceleration and guides them towards the correct approach.
  
  Label: question-and-answer