# Homework Help: Impact force question

1. Aug 31, 2007

### cow

Heya,

I need help answering a question:

If i drop an object that weighs 100 pounds from a height of 6 feet what will be the impact in pounds when the object hits the ground (assume that the ground is a hard surface)?

Thanks for any help that you guys can provide.

edit:

I just want to say that this is NOT a homework question. Just a question that my dad needs answered. We looked through an old college physics text book I have but were not able to come up with an answer.

Last edited: Aug 31, 2007
2. Sep 1, 2007

### PhanthomJay

There is no such thing as a perfectly rigid surface. All materials must deform at least a small amount when a force is applied. The amount of this deformation during impact determines the time and force of impact...the greater the deformation of the contacting surfaces, the less the impact force. So your question is not answerable in the absence of other data. The object, neglecting air resistance, will hit the ground at about 20 ft/sec, and come to a stop in a short time. The impact force will likely be several thousand pounds or more, depending on what that stop time (and deformation) is. For example, if it came to a stop in 0.01 seconds, then F=m(delta v)/t = approximately
(100/32)(20)/0.01 = 6000 pounds. If the ground/object were harder or softer, , that force could significantly increase or decrease since the contact time would be different.