If an object weighing 1lb is dropped from a height of 90 feet, what is the force with which it will impact on?

Question

safety issue

Answer 1

In addition to the height of the drop and the weight, the impact force is a function of how quicly the weight stops when it impacts. As the object falls it is converting potential energy (altitude) into kinetic energy (velocity). The total energy is the product of the weight and the fall distance. Here that is 90 ft-lbs.

If the object impacts some cushion so that it takes 1 foot to come to a stop, the average force acting over that one foot is 90 lbs. If it stops in 6 inches the average force is 180 lbs. The cushion must absorb the 90 ft-lbs of kinetic energy to bring the object to a halt so the average force multiplied by the stopping distance will be 90 ft-lbs.

If the object is stopped quickly, the force can be pretty high. A great example of this is a hammer hitting a nail. Say the hammer weighs 1 lb and is travelling at 40 feet per second (this gives an energy of 6.2 ft-lbs but I won't expain how to get that here) when it hits the nail. If the nail is driven in 1/4" by the impact, the average force is 300 lbs. The average impact force is the kinetic energy divided by the stopping distance so large forces are possible if the stopping distance is small.

Answer 2

It is not possible to answer your question as is.

There are a lot of unknown variables here; local gravitational force, air density, wind speed, the object's coefficient of drag, the resilience of the ground, and especially the density (or specific gravity) of the 1 lb object.

Clearly, a 1 lb block of styrofoam on a windy day will hit the ground with a lot less force than a 1 lb solid ball of lead. That is because the air will have a much greater effect on the styrofoam than on the lead ball. The earth's gravitational pull is equal on both the styrofoam and the lead ball (if they are both one pound) but the air resistance is much higher on the styrofoam. Therefore the terminal velocity of the lead ball will be many times more than the styrofoam. So you really need to provide the density of the object and the other variables to come up with the right answer.

The only way that the density, shape, and atmospheric conditions are not critical factors in determining the impact force on the ground would be in a vacuum. In a vacuum, the formula F=ma would apply.

Answer 3

It will accelerate at a rate of 9.81 metres per second squared. Use the mass x velocity formula to calculate the force. Don't forget to convert all your units.

Answer 4

use the momentum eq.

Answer 5

f=ma

1lb * 32.2 ft/s^2
= 32.2 lb-ft