Home › AP Physics 1 › Physics › Work, Energy, and Energy Resources › A person holds a heavy briefcase perfectly still…
A person holds a heavy briefcase perfectly still at their side, with no motion at all. According to the scientific definition of work, how much work does the person's arm do on the briefcase, and why do their muscles still get tired?
AZero work, since displacement is zero, though muscles work against each other
BA large positive amount of work, proportional to the force exerted
CNegative work, since holding something still opposes gravity
DIt cannot be determined without knowing the briefcase's mass
Answer & Solution
Correct answer: A. Zero work, since displacement is zero, though muscles work against each other
1. Work requires displacement, W = F d cos theta, and here the displacement d of the briefcase is zero.
2. Because d = 0, the work done on the briefcase by the person's arm is exactly zero, no matter how large the supporting force is.
3. The tiredness comes from the muscles doing work against one another internally, not from any work being done on the briefcase itself.
4. The work is not a large positive amount, nor negative, and knowing the briefcase's mass would not change the fact that zero displacement forces the work to be zero.
_Source: OpenStax College Physics (CC BY 4.0), Ch 7 "Work, Energy, and Energy Resources", section 7.1 Work: The Scientific Definition_
Related questions
China's energy mix differs sharply from that of most Western countries. What fuel dominateOnly 10% of United States electricity is generated by renewable resources. Which renewableMost countries rely heavily on nonrenewable resources for electricity, but some meet a larRenewable energy sources include water, wind, solar, and biomass, since these cannot be usThe United States has 4.5% of the world's population. According to world energy use figureAmong the principal energy resources used worldwide, which single fuel supplies about 40% A surprisingly large share of all the energy the human body consumes goes toward a purposeUseful work, as defined for a person's activities, includes climbing stairs or acceleratin