Physics
Physics
Problem
Four identical crates—labeled A, B, C, and D—each rest on a flat warehouse floor. At a certain instant, workers apply horizontal pushes of different magnitudes and directions to the crates. Air resistance is negligible, and each crate experiences kinetic friction of opposite its motion at that instant. The table below lists, for each crate, the magnitude and direction of the applied push and the direction in which the crate is moving at that instant. Crate | Applied push (magnitude, direction) | Direction of motion at that instant A | , east | east B | , east | east C | , west | west D | , west | east (a) For each crate, draw a clearly labeled horizontal-axis force diagram showing the applied push and the kinetic friction force. (b) Determine the magnitude of the net horizontal force on each crate. (c) Rank the crates from greatest to least according to the magnitude of the net horizontal force acting on them. If any crates tie, indicate that explicitly. (d) Identify which crates, if any, are in translational equilibrium at the instant described. Provide a concise justification for each crate based on your force analysis.Intuitive explanation
The key is recognizing that friction always opposes the direction of motion, not the applied force. For each crate, you need to find the net force by carefully adding the applied push and friction as vectors—they point in opposite directions only when the push and motion align. Once you have the net force, you can determine whether each crate is accelerating, decelerating, or moving at constant velocity.
Intuitive explanation
The key is recognizing that friction always opposes the direction of motion, not the applied force. For each crate, you need to find the net force by carefully adding the applied push and friction as vectors—they point in opposite directions only when the push and motion align. Once you have the net force, you can determine whether each crate is accelerating, decelerating, or moving at constant velocity.