A 5.0 kg wooden crate initially at rest on a level loading dock is moved through the…
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A 5.0 kg wooden crate initially at rest on a level loading dock is moved through the following three consecutive displacements:
Segment 1: Dragged 4.0 m due east along the horizontal dock surface by a worker who pulls with a constant 100 N force directed 45° above the horizontal. Friction is negligible.
Segment 2: Without changing horizontal position, the crate is lifted straight upward 2.0 m at constant speed by a hoist cable that exerts only vertical forces.
Segment 3: The crate is then lowered straight back down the same 2.0 m to its original vertical position at constant speed, again by the hoist cable.
Ignore any motion other than that described.
(1) For each segment, determine the sign (positive, negative, or zero) of the work done on the crate by the gravitational force and calculate its numerical value.
(2) For each segment, calculate the work done by the worker’s applied force (segment 1) and by the tension in the hoist cable (segments 2 and 3), indicating the sign in each case.
(3) Compute the net work done on the crate over the entire three-segment path. Explain how your result is consistent with the crate’s initial and final kinetic energies.
(4) Comparing your answers for gravitational work in segments 2 and 3 with those for the cable tension, discuss how the conservative or non-conservative characteristics of these forces are reflected in their work over the closed vertical path.