Minimum Acceleration for Sliding Cream Pie: Solving Static Friction Problem

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Homework Help Overview

The problem involves determining the minimum acceleration required to prevent a cream pie from sliding down a vertical hand, given the coefficient of static friction between the hand and the pie. The context is rooted in static friction and forces acting on an object in equilibrium.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants discuss the forces acting on the pie, including weight, normal force, and friction. There are attempts to relate these forces to the equations of motion, with some questioning the necessity of the pie's mass in the calculations.

Discussion Status

The discussion is ongoing, with participants providing insights and guidance on analyzing the forces involved. Some participants express confusion about the relationships between static friction, normal force, and acceleration, while others attempt to clarify these concepts. There is no explicit consensus yet on the correct approach or solution.

Contextual Notes

Participants note the absence of the pie's mass in the problem statement, leading to discussions about how this affects the normal force and overall calculations. There are references to equilibrium conditions and the need for further verification of results.

Jericho_15
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Homework Statement


The coefficient of static friction between your hand and a pie is 0.70. if you want to put a cream pie pie in someone's face, what is the minimum acceleration needed to keep it from sliding down your vertical hand?

The Attempt at a Solution


Im not sure how to go about this.. but I am prttty sure that is related to F=ma..
Help would be greatly appreciated, thanks a lot..
 
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draw a free body diagram of the PIE-mass, what forces acting downwards what forceas acting upwards? what force is the hand "pushing the" pie-what is the normal force?

answer those questions, and see if it helps , answer them and I'll help You from there.
 
ok.. i know the normal force is acting upwards, and weight is acting downwards, and there is also the force of the hand pushing on the pie.. but they don't give me a mass fro the pie.. so wouldn't that mean the normal froce and the wight cancel each other..
 
1)Normal force= perpendicular to the surface(the hand) look at this in this way:
hand pushes on Pie, Pie pushes same force on hand(third law of...)=Normal force direction=Left.
2)upwards-friction. moment before it slides fs=Us * N
N=normal force=(this is the key for the problem, try to figure out by your own).
Write forces in the Y direction, and in equilibrium Fy=0

Good Luck!

P.S
Mass of Pie will cancel out
and the solution is for vertical hand:
|=hand
X=Pie
_
X|
X|
X|
 
Last edited:
Don't forget to experimentally verify the result of the calculation.
 
ok, i think I am starting to figure it out... you have to take Us/g and that equals Fs
 
"Don't forget to experimentally verify the result of the calculation."
xD I would've preferred eating the pie :D
You're close to the answer :}
Write Your equations
btw there was a mistake in my last post
i wrote fs=us*m*n , its us*N

I'm off now, good luck solving, other ppl can help you for now :
good luck.
 
Last edited:
Fs= Us * M*N
Fs= Us *M/mg
Fs=Us/g
Fs=.0713

no i take the Fs and plug it back in right
so now i do this:
Fs=Us*n
Fs/Us=n
.0713/.70=.101
n=.101
so that would mean since N=.101
acceleration is also equal .101n
 
Last edited:
Is anyone elsehere that can help me..
 
  • #10
check my last post.
fs=us*N.
N=m*a.
What You've done is wrong Imo.
 
  • #11
ok if what ur saying is true, then that would mean Fs and Us are equal, and my acceleration would be 1.. but i think that wouldn't make sense... corret me if I am wrong.
 
  • #12
I really wonna sleep xD
fs=static friction=MG(in equilibrium state)=us*N
how did yo get that they're equal (fs and us).

Hope You see this:
mg down, friction up which depends on the normal force, normal force acting on hand (and by hand on body).
good luck.
 
  • #13
i still can't get it... anyone else can help me cause I am stuck...
 

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