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
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top