What Is the Critical Angle to Keep a Box Moving with Kinetic Friction?

[aftershock]

while moving in, a new homeowner is pushing a box across the floor at constant velocity. the coefficient of kinetic friction between the box and the floor is 0.41. the pushing force is directed downward at an angle (theta) below the horizontal. when theta is greater than a certain value, it is not possible to move the box, no matter how large the pushing force is.

find that value of theta.


I tried this.

P= pushing force
x = theta
m = mass of box
g= 9.8 or accel of gravity

Pcosx = (Psinx +mg).41

no luck :(

 

[willem2]

P= pushing force
x = theta
m = mass of box
g= 9.8 or accel of gravity

Pcosx = (Psinx +mg).41

no luck :(

Well you're nearly there. If the pushing force is very large then Psinx >> mg and you can ignore
the weight of the box.