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Given the mass, angle, and the coefficient of static friction, find the pulling force

by nina123
Tags: angle, force, friction, mass, pulling
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nina123
#1
Oct7-12, 09:45 PM
P: 5
1. The problem statement, all variables and given/known data

A father gives his daughter a ride on a sled by applying a force F at an angle θ = 26.0░ with respect to the horizontal. If the coefficient of static friction is Ás = 0.153, and the combined mass of sled and child is m = 24.0 kg
What is the minimum amount of force required to move the sled from rest by
pulling it

2. Relevant equations

F=ma

3. The attempt at a solution

I have tried multiple ways and i keep getting the wrong answer,
I think i should take the sum of all the forces in the x direction and of the y direction and somehow get the force i need but im not exactly sure.

HELP PLEASE?
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution
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runningninja
#2
Oct7-12, 09:55 PM
P: 26
The words "minimum amount of force" and "from rest" imply that this is a statics problem. In statics, what is the special condition on the net force? What does the word "static" imply about the value of the acceleration in f=ma?
Once you figure that out, you should have your net x force components (which requires trig) sum to this special value for the net force as well as you net y force components (which also requires trig).
EDIT: Also make sure you have your pulling force in the correct direction. Did you draw a free body diagram?
nina123
#3
Oct7-12, 10:06 PM
P: 5
Quote Quote by runningninja View Post
The words "minimum amount of force" and "from rest" imply that this is a statics problem. In statics, what is the special condition on the net force? What does the word "static" imply about the value of the acceleration in f=ma?
Once you figure that out, you should have your net x force components (which requires trig) sum to this special value for the net force as well as you net y force components (which also requires trig).
So "static" would imply that the value of acceleration =0 ?right?

so i have in the x direction:
F(pull,x) + F(friction,x) +W(x) + n(x) = 0
but there is no W or F(gravity) in the x direction so that equals zero and same for n(x) (normal force) =0.
therefore i have:
F(pull,x) +f(friction,x)=0 right?

In the y direction:
F(pull,y) + F(friction,y) +W(y) + n(y) = 0
F(friction,y)=0
therefore i have:
F(pull,y) +W(y) + n(y) = 0 right?

then F(pull,x) = F(pull)cosθ
and F(pull,y) =F(pull)sinθ

I all that ive said is correct now, what would i do now? or is there other things that i am missing ?

runningninja
#4
Oct7-12, 10:41 PM
P: 26
Given the mass, angle, and the coefficient of static friction, find the pulling force

Since the force is pulling, is your pulling force positive or negative? Is your weight positive or negative?
I see two equations and two unknowns (Fpull and normal). Pull out your algebra toolkit and solve it.
nina123
#5
Oct8-12, 02:36 PM
P: 5
thanks for your help, i got the answer :P


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