Question

A packing crate is sitting at rest on an inclined loading ramp. How does the magnitude of the force of static friction compare to the other forces acting on the crate?

Answer 1

As a crate is resting on the inclined surface of the ramp we have following forces on the crate

1. Weight of the crate vertically downwards

2. Normal force due to ramp perpendicular to the surface

3. static friction force along the ramp upwards

so here we know that crate is at rest

so we can say that

normal force is balanced by component of weight of crate

so we have

$N = mg cos\theta$

also we can say that friction force is balanced by another component of weight of the crate

$F_f = mg sin\theta$

so friction force is less than the weight of the crate and it will act opposite to it