Three friends who each have a mass of 65 kg reach a lecture hall that is located 5.0…
PHYSICS · Multi-part · CBSE · Physics · Work and Energy · Work and Energy
Problem
Three friends who each have a mass of 65 kg reach a lecture hall that is located 5.0 m above street level by three different routes.
• Student A sprints up a flight of stairs and reaches the doorway in 4.0 s.
• Student B walks up the same stairs and arrives 10 s after leaving street level.
• Student C stands motionless on an escalator that carries her the same vertical distance in 20 s.
Assume any horizontal motion is negligible so that the only change in mechanical energy is gravitational potential energy.
(a) Rank the three students from greatest to least average mechanical power output required to raise their bodies, clearly explaining your reasoning.
(b) Student B returns to street level, picks up a 12 kg backpack, and then walks up the stairs again in the same 10 s. Describe qualitatively how carrying the backpack changes Student B’s average power output, and justify your answer without performing a numerical calculation.
(c) Suppose the escalator suddenly stops halfway, forcing Student C to climb the remaining distance up the stationary escalator in an additional 6.0 s. Compare the average power output for Student C over the entire trip with the value you ranked in part (a), and justify your comparison.