A block placed on a horizontal surface is being pushed by a force F making an angle θ with the vertical. If the friction coefficient is μ, how much force is needed to get the block just started.
F=
The situation is shown in figure.In the limiting equillibrium the frictional force f will be equal to μN.
For horizontal equillibrium
F sinθ = μN
For vertical equillibrium
Fcosθ + mg =N
Eliminating N from these equations,
Fsinθ=μFcosθ +μmg
F=μmgsinθ−μcosθ