Bungee Jumping: Reasonable Assumptions for College Student's Adventure

[philo51]

A bored college student decides to try bungee jumping. He attaches an elastic bungee cord to his ankles and happily jumps off a tall bridge across a river. He ends up barely touching the water before the cord jerks him back up

The length of the relaxed cord is y_e; the distance from the bridge to the river surface is y_0 (where y_o>y_e), and the spring constant of the elastic cord is k.

Which assumptions are reasonable to make in this problem?

a.The student can be treated as a particle moving with constant speed.
b.The student can be treated as a particle moving with constant acceleration.
c.The student cannot be treated as a particle.
d.The air resistance is substantial.
e.The air resistance is negligible.
f.The amount of heat generated in the bungee cord is substantial.
g.The amount of heat generated in the bungee cord is negligible.
h.The bungee cord applies a constant (or zero) force on the student.
i.e bungee cord can be modeled as a spring that obeys Hooke's law.

i put B,E,G,I and that was wrong. any suggestions?

 

[HallsofIvy]

He ties the bungee cord to his ankles. What part of his body "barely touches the river"? What is the distance between his ankles (the end of the bungee cord) and the surface of the river at that instant? What's wrong with treating him as a "particle"?

 

[thepatientmental]

Based on the given scenario, the following assumptions are reasonable to make:

a. The student can be treated as a particle moving with constant speed.
b. The student can be treated as a particle moving with constant acceleration.
e. The air resistance is negligible.
h. The bungee cord applies a constant (or zero) force on the student.
i. The bungee cord can be modeled as a spring that obeys Hooke's law.

Assumptions c, d, f, and g are not reasonable in this scenario. The student can be treated as a particle because they are only concerned with their vertical motion, and the air resistance can be neglected since it is not mentioned in the problem. The bungee cord can be modeled as a spring because it follows Hooke's law, which states that the force applied is directly proportional to the extension of the cord. However, the student cannot be treated as a particle moving with constant speed, as their speed will change due to the force of the bungee cord. Similarly, the student cannot be treated as a particle moving with constant acceleration, as the acceleration will also change due to the force of the bungee cord. Finally, the amount of heat generated in the bungee cord is negligible because the cord is designed to withstand the forces and does not generate a significant amount of heat. Therefore, the most reasonable assumptions for this problem are a, b, e, h, and i.