# 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
The text passage is a physics homework problem and solution attempt, focusing on the forces acting on a box of oranges being pushed across a floor. The student is trying to determine the coefficient of friction and is confused about the role of acceleration in the problem.
no_question

while the passage discusses a physics problem, it does not explicitly pose a mathematical question that requires a numerical answer. the student is seeking conceptual clarification rather than a specific calculation.
Given a text passage, determine:
    1. If it contains a mathematical question (including word problems or calculations)
    2. If an answer to that mathematical question is provided in the text

First, describe the content structure you found in 1-2 sentences.

Then provide your analysis in the following format:
TYPE: <one of the following values>
- NO_QUESTION
- SINGLE_QUESTION
- SINGLE_QUESTION_WITH_ANSWER
- MULTIPLE_QUESTIONS
- MULTIPLE_QUESTIONS_WITH_ANSWERS
system
# 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
user
The text passage is a physics homework problem and solution attempt, focusing on the forces acting on a box of oranges being pushed across a floor. The student is trying to determine the coefficient of friction and is confused about the role of acceleration in the problem.

TYPE: NO_QUESTION

While the passage discusses a physics problem, it does not explicitly pose a mathematical question that requires a numerical answer. The student is seeking conceptual clarification rather than a specific calculation.