Calculating speed in water taking drag force into account

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SUMMARY

The discussion focuses on calculating the time it takes for a diver to reach 2% of their original speed of 6.5 m/s after hitting the water, considering a drag force defined by Fd = (−1.00×104 kg/s) v. The diver's mass is 75 kg, and the problem requires applying Newton's second law to formulate a differential equation that relates acceleration and velocity. The solution involves deriving velocity as a function of time, which is essential for determining the time to reach the specified speed.

PREREQUISITES
  • Understanding of Newton's second law of motion
  • Knowledge of differential equations
  • Familiarity with drag force concepts in fluid dynamics
  • Basic principles of kinematics
NEXT STEPS
  • Study the derivation of velocity as a function of time in drag force scenarios
  • Learn about solving first-order differential equations
  • Explore the effects of drag force on motion in fluids
  • Investigate numerical methods for solving complex motion equations
USEFUL FOR

Physics students, engineers, and anyone interested in fluid dynamics and motion analysis will benefit from this discussion.

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Homework Statement



You dive straight down into a pool of water. You hit the water with a speed of 6.5 m/s, and your mass is 75 kg. Assuming a drag force of the form Fd = (−1.00×104 kg/s) v, how long does it take you to reach 2% of your original speed? (Ignore any effects of buoyancy.)

Homework Equations



?

The Attempt at a Solution



no ideas whatsoever
 
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First, write down Newton's second law. On one side we have acceleration, which is the first derivative of velocity, and on the other side, we have velocity, so this is a differential equation. (Don't forget about gravity.) Solve this differential equation to get velocity as a function of time. This should get you started.
 

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