Calculating Force in Freefall with Terminal Velocity

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Discussion Overview

The discussion revolves around calculating the force with which a body in freefall would hit the ground after reaching terminal velocity. Participants explore various approaches to determine this force, considering factors such as mass, impact time, and distance of impact.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that the force of impact can be calculated by multiplying the mass of the object by its velocity at impact.
  • Others argue that to accurately determine the force, one must consider either the distance the object penetrates into the ground or the time taken for the impact, using formulas like F = mv/t or F = (mv^2)/2d.
  • A participant points out that the initial velocity divided by the time of impact gives acceleration, which when multiplied by mass yields the force.
  • Several participants acknowledge mistakes in their previous statements, indicating confusion between concepts of force and energy.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct method for calculating the force of impact, with multiple competing views and corrections being presented throughout the discussion.

Contextual Notes

Some responses indicate a reliance on specific assumptions, such as the final velocity being zero and the nature of the landing area, which may affect the calculations. There is also mention of potential confusion between different physical concepts.

sweenep
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If a body is in freefall and has reached its terminal velocity say 56 metres/s, its acceleration is zero, how do you work out with what force it would hit the ground
 
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you know the terminal velocity,that velocity divided by the time the body took to come to rest on hitting the ground would be the force with which it would hit the ground
 
sweenep said:
If a body is in freefall and has reached its terminal velocity say 56 metres/s, its acceleration is zero, how do you work out with what force it would hit the ground
Should be just mass of falling object times speed with which it impacts. You should probably, for the sake of simplicity, assume that the landing area has no elastic properties. The force would be the same even if the thing lands in a bowl of Jell-O, but it would be distributed a lot differently.
 
Last edited:
Beg your pardon, but the last two responses are incorrect.

If you have the initial speed of impact, you will need the mass of the object PLUS either the distance that the object went onto the ground during impact, or the time interval of the impact with the ground.

IF you have the time of the impact, F = mv/t , where v is the "change in velocity" (final velocity is zero). This is using the impuolse-momentum theorem.

If you are given d, the distance of impact (depth of crater), F = (mv^2)/2d
This is using kinematics and dynamics
 
well hello!your first option is what I wrote!
 
Your response is missing the mass of the object. The initial velocity divide by time of impact (assuming final velocity is zero) gives the acceleration. Multiply acceleration times mass to get force.
 
oh!I made a mistake
 
nishant said:
oh!I made a mistake
Shhh! It happens.
 
it better not happen often
 
  • #10
Well, if I had a nickel for every mistake I've made in responding here, heck, I'd have fifteen cents by now.
 
  • #11
Chi Meson said:
Beg your pardon, but the last two responses are incorrect.
I cannot believe that I confused 'force' and 'energy'. :redface: Sorry, guys. The terms just kind of swapped places in my head and I didn't notice. It's like when I'm stuck on a crossword puzzle answer for hours, then suddenly realize that I've misread the clue eight times in a row. (In my defense, I was on my 7th beer at the time.) :biggrin:
 

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