## 20161125

### Physics midterm problem: Resident Evil: Apocalypse rope descent

Physics 205A Midterm 2, fall semester 2016
Cuesta College, San Luis Obispo, CA

Resident Evil: Apocalypse
(Constantin Film, 2004)

In the movie Resident Evil: Apocalypse (Constantin Film, 2004) Milla Jovovich (mass 59 kg[*]) vertically descends 99.5 m down the east tower of the Toronto City Hall[**] starting from rest, reaching a final speed of 5.0 m/s using a device that continuously exerts a constant friction force on the rope controlling her descent. Consider her and the rope to be a single object as she descends. Ignore drag, stretching in the rope, the mass of the rope, and any contact between her feet and the side of the building. For this process, determine (a) how much energy was lost to friction, and (b) the magnitude of the friction force on the rope. Show your work and explain your reasoning using the properties of forces, work, energy forms and (non-)conservation of energy.

[*] healthyceleb.com/milla-jovovich-height-weight-body-statistics/1252.
[**] wki.pe/Toronto_City_Hall.

Solution and grading rubric:
• p:
Correct. Determines:
1. the total work done by friction against the motion of Milla Jovovich, by setting up an energy/transfer equation, and solving for the net change in her (increasing) translational kinetic energy and (decreasing) gravitational potential energy;
2. solves for the magnitude of the friction force by dividing the work done by friction by the displacement (and the cosine of the angle between these directions when drawn tail-to-tail).
• r:
Nearly correct, but includes minor math errors. Typically finds the total work done by friction, some attempt at finding the magnitude of the friction force with conceptual errors.
• t:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Typically finds the total work done by friction, no substantive approach to finding the magnitude of the friction force.
• v:
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. At least some systematic attempt at using energy changes and work.
• x:
Implementation of ideas, but credit given for effort rather than merit. No clear attempt at applying energy changes and work.
• y:
Irrelevant discussion/effectively blank.
• z:
Blank.
Sections 70854, 70855, 73320
Exam code: midterm02oPt0
p: 19 students
r: 11 students
t: 20 students
v: 5 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 1317):

Another sample "p" response (from student 6969):