Homework Help: Kinetic friction find greatest acceleration

1. Oct 14, 2008

Sneaky07

1. A crate resting on a rough horizontal floor is to be moved horizontally. The coefficient of kinetic friction is 0.40. To start the crate moving with the least possible applied force, in what direction should the force be applied?

a. Horizontal

b. 24 degrees below horizontal

c. 22 degrees above the horizontal

d. 24 degrees above the horizontal

e. 66 degrees below the horizontal

Formulas I used.
2. (Normal force) Fn = m*a
(Kinetic frictional force) Fk = (uk)*|Fn| (uk being coefficient of kinetic friction)

Work I did.
3. Figured out the normal force which was m*a*cos(theta). After I multiplied it by the (uk) and got kinetic frictional force but don't know where to go from there...

Thanks in advance!!

2. Oct 15, 2008

tiny-tim

Welcome to PF!

Hi Sneaky07! Welcome to PF!

(have a theta: θ and a mu: µ )

However did you get m*a*cos(theta)?

Hint: this is a straightforward Newton's second law problem …

call the force "F", then take vertical components and horizontal components (separately), to get two equations for F.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook