# Dropping objects air resistance

1. Aug 17, 2013

1. The problem statement, all variables and given/known data
A creature of mass $m$ and bottom surface area of $A$ is dropped from a height $h$ towards the ground. The creature dies if a force of $F_K$ or greater acts on it. What is the value range of acceleration due to gravity, $g$, for such creature to survive the fall?

2. Relevant equations

Surely the problem requires air resistance since mass and surface area are mentioned. I think this can be modelled as $F_D=-k \cdot v$ unless anyone has any better ideas?

3. The attempt at a solution

The question is what else to do - we'll need a differential equation, then to solve it for $g$ in terms of $F_K$, $h$, $m$ and $A$ (probably work out the terminal velocity first and then relate it to $F_K$ and $g$)? I hope we can assume that height $h$ is sufficient that terminal velocity will be reached. If not, we might have to use something more fundamental.

2. Aug 17, 2013

### rude man

Depends on the softness of the ground. Use the impulse formula. F*Δt = Δp and Δt =√(2s/g). But you need to know s, the distance over which the fall was cushioned, i.e. the softness of the ground.

The presence of A in the problem statement does suggest that air resistance was to be considered. Could be a red herring. I would ignore it or get an explanation from the instructor.