# Homework Help: Determining the force of something that is dropped.

1. Nov 6, 2005

### wasteofo2

What formula might I use to determine the force something has when it strikes the ground after being dropped? I initially thought to just use F=ma, but I can't just plug in 9.8m/s^2, cause that would yeild the same answer regardless of the height it was dropped from.

Any help?

Thanks,
Jacob

2. Nov 6, 2005

### Staff: Mentor

You need to know some characteristics of the impact. The harder the object and the surface, the shorter the impact, and therefore, the higher the force.

3. Nov 6, 2005

### Kazza_765

It depends on the time over over which it occurs, which will depend on the object and what it is landing on (there will be a much larger force if it lands on concrete as opposed to ice cream (mmm.. ice cream)).. But if you can estimate that, then Force * Time is equal to the change in momentum of the object. You can work out its inital momentum using the equations of motion, and assume that its final momentum is equal to zero (unless it is bouncy).

4. Nov 6, 2005

### wasteofo2

So it'd be pretty impossible to figure it out unless you had data for the specific objects and surfaces you were dealing with, right? If I could figure out the time of the impact, would I also need to know the acceleration at the initial point of impact, or would velocity be enough?