A delivery boy raises a $10$ kg sack to a $2$ m shelf in $4$ s. The power expended (using $g = 10$ m/s$^2$) is:
A$10$ W, ignoring the height factor in the lift
B$200$ W, equal to the total work without dividing by time
C$80$ W, since $P = mgh$ alone gives this for the shelf
D$50$ W, since $P = mgh/t = 200/4 = 50$ W
Answer & Solution
Correct answer: D. $50$ W, since $P = mgh/t = 200/4 = 50$ W
$W = mgh = 200$ J; $P = W/t = 200/4 = 50$ W.
Related questions
A crate dragged across a rough floor loses mechanical energy because friction is:Conservation of mechanical energy is the form the work-energy theorem takes when the forceCalculating work for a conservative force is easier than for a complicated path because itA force acting entirely perpendicular to an object's displacement does how much work?Mechanical energy transferred into or out of a system equals the work done by an external Winding up a toy or an old-fashioned watch stores energy by doing work against its:Which three energy examples are named together?The kinetic energy in the work-energy theorem is specifically the translational kinetic en