- #1
gijungkim
- 50
- 2
Homework Statement
The total force needed to drag a box at constant speed across a surface with coefficient of kinetic friction Uk is least when the force is applied at an angle theta such that
a.sin(theta) = Uk.
b.cos(theta) = Uk.
c.tan(theta) = Uk.
d.cot(theta) = Uk.
e.sec(theta) = Uk.
Homework Equations
F = ma
Ff = Uk * Fn = m*g*Uk
Fx = F *cos(theta)
Fy = F*sin(theta)
The Attempt at a Solution
First the answer is d. cot(theta) = Uk
I tried to solve it, but couldn't figure it out...
This is my work
Since it is dragged at constant speed, the acceleration is 0. So a = Ftotal/m = 0
Ftotal = F*cos(theta) - (mg - F*sin(theta))Uk = 0
F*cos(theta) / (mg - F*sin(theta)) = Uk... which is wrong...
Can anyone help me?