# SoLid Pressure on this case

1. Apr 4, 2005

### LasTSurvivoR

Ok guys everyone knows teh solid Pressure = P / S but i have a question..
I though about an object that falls from 20 meters.(Its mass is 2 kg, 2x2x2 meters cube)
When it reaches the ground how much pressure does it make , in normal case
20 . 10 / 2² = 50 Pascal it makes.However how can I calculate the pressure made by a falling object that has a downwards velocity ?

THankkss , that can be a foolish question but I couldnt understand this.

2. Apr 4, 2005

### Andrew Mason

It depends on how long it takes to stop. It is just a mechanics question involving change of momentum.

[Corrected:]

$$F = mg + mv/\Delta t$$ (assuming constant stopping force)

$$P = F/A = \frac{mg + mv/\Delta t}{A}$$

AM

Last edited: Apr 4, 2005
3. Apr 4, 2005

### LasTSurvivoR

Thanks that is a very logical thought , and probably the correct one I had never thought this :) I will Try :=)

4. Apr 4, 2005

### Crosson

Those equations are alittle messed up andrew, they say that the force decreses the faster you stop :)

It should be:

$$F = mg + \frac{mv}{\Delta t}$$

$$P = F/A = \frac{mg + \frac{mv}{\Delta t}}{A}$$

v is the velocity at the time of impact, which you can find from kinematics.

For the record, this equation assumes no bouncing.

5. Apr 4, 2005

### Andrew Mason

Right you are! $F\Delta t = mv$

AM