Question

A factory worker pushes horizontally to the right on a 250 N crate with a force of P = 75.0 N on a horizontal rough floor. A 135 N crate rests on top of the one being pushed and moves along with it. Call the bottom crate {\rm A} and the top crate {\rm B}.Make a free-body diagram of the crate {\rm A} if the total friction force is less than the worker's push.

Answer 1

First, draw a coordinate axis. This is essential and fundamental to any FBD.

Second, draw a box. Place a point in the middle of the box. This is the box's center of mass. We will assume all forces act through this point, as the box doesn't roll and instead simply slides.

Third, draw an arrow directed left. This is the force exerted by the worker.

Finally, draw an arrow directed right. This is the force of friction. Friction always opposes motion.