A ball of mass is dropped from rest from a balcony above the ground
PHYSICS · Single correct · AP · Physics 1: Algebra-based · Work Energy and Power · Work Energy and Power
Problem
A ball of mass m is dropped from rest from a balcony 10m above the ground. Student A defines gravitational potential energy to be zero at the balcony, whereas Student B defines it to be zero at the ground. Both students use conservation of energy to predict the speed of the ball just before it strikes the ground.
Which of the following best explains why both students obtain the same speed?
(a) Because the ball’s final speed depends only on g, not on where zero potential energy is chosen.
(b) Because kinetic energy is completely independent of the numerical values chosen for potential energy.
(c) Because the change in potential energy ΔU=mgΔh is the same for both reference choices, and only the change enters the energy equation.
(d) Because gravitational potential energy is always negative no matter where the zero level is placed, so both students substitute the same value.