physics
posted by Rose on .
A 90Kg box is pushed by a horizontal force F at constant speed up a ramp incined at 28 degrees. Determine the magnitude of applied force when the ramp is frictionless and when the coefficient of kinetic friction is 0.18

xaxis  along the ramp, yaxis  perpendicular to the ramp (upwards).
x: F =F(fr) + m•g•sinα,
y: N=mgcos α,
F=μ•N + m•g•sinα = μ• m•g•cos α + m•g•sinα =m•g(μ• cos α+ sinα)