Are the answers correct? I feel that the friction force is wrong with number 3.
Hey Stuck Man.
Just a question about the friction: is the friction a two way force (in other words, if you drag something both up and down the ramp does it oppose it both ways)?
If this is the case you might want to check out the friction vector for number 4 since it implies that friction actually helps the object go up the ramp.
As far as friction is concerned, kinetic friction is easy: it's always opposing the motion of the object. Static friction is a little harder, but consider for diagram 3...The problem states that the object is going to be moving up the slope. So the friction force is down the slope.
So why is the friction going up the slope in problem 4?