Solve for Pulling Force for Sled w/ Mass, Angle, & Coeff. of Friction

AI Thread Summary
To determine the minimum force required to move a sled with a child from rest, the problem involves analyzing forces in both the x and y directions, considering the angle of pull and the coefficient of static friction. The condition of static implies that the acceleration is zero, leading to the equations of equilibrium for both directions. The pulling force can be broken down into its x and y components using trigonometric functions. After establishing the equations, the solution involves algebraically solving for the pulling force while accounting for the normal force and friction. The discussion concludes with the successful calculation of the required pulling force.
nina123
Messages
5
Reaction score
0

Homework Statement



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 µs = 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

Homework Equations



F=ma

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 I am not exactly sure.

HELP PLEASE?
 
Physics news on Phys.org


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?
 


runningninja said:
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 I've said is correct now, what would i do now? or is there other things that i am missing ?
 


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.
 


thanks for your help, i got the answer :P
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Back
Top