Speed of a sphere fired straight up, including quadratic air resistance

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SUMMARY

The discussion focuses on calculating the speed of a sphere with a radius of 0.2 cm fired straight up, incorporating quadratic air resistance. The quadratic air resistance is defined by the equation FR = cv², with a drag coefficient c of 4.05 x 10⁻⁶. Participants emphasize that the acceleration is not constant due to the variable nature of air resistance, necessitating a more complex approach to modeling the sphere's motion. The correct formulation involves recognizing that acceleration is a function of velocity, requiring a differential equation to solve for the sphere's speed upon returning to the ground.

PREREQUISITES
  • Understanding of quadratic air resistance and its mathematical representation
  • Familiarity with basic kinematics and the equations of motion
  • Knowledge of differential equations and variable acceleration
  • Experience with physics concepts related to projectile motion
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  • Study the derivation of equations for motion under quadratic air resistance
  • Learn how to solve differential equations involving variable acceleration
  • Explore numerical methods for simulating projectile motion with air resistance
  • Investigate the impact of different drag coefficients on projectile trajectories
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Physics students, educators, and anyone interested in advanced projectile motion analysis, particularly in contexts involving air resistance and differential equations.

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Homework Statement


A sphere of radius 0.2 cm is fired straight up with speed v0. What is its speed when it hits the ground? (Include quadratic air resistance but ignore linear air resistance.)

Homework Equations


Quadratic air resistance: FR = cv2
c = 0.5CpA = 4.05 x 10-6

The Attempt at a Solution


I figured as the sphere rises, its velocity can be modeled as v = v0 - gt - cv2t/m. As it falls, velocity can be modeled as v = gt - cv2t/m. Other than that, I'm not really sure where to go.
 
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Hi soundbyte, welcome to PF

I don't think you can write the velocity like that, as the equation

v = v0 + a.t is for constant acceleration only,

in this problem a varies with v and v=v(t), so a= a(t)...(ie a is a function of t)

A good place to start would be to write the acceleration on the sphere as a function of v based on the forces
 

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