# [Blindmath] physics/mathematics problem; have a solution?

Richard Baldwin baldwin at dickbaldwin.com
Sun Dec 18 23:30:38 CST 2011

```A quick off the top of my head assessment tells me that there is a missing
term.

The force required to stop the mass is equal to the mass times the negative
acceleration.

The negative acceleration is equal to the change in velocity from impact
velocity to zero velocity in a given amount of time. Since we don't know
the time interval over which the velocity changed, we can't compute the
acceleration. If the time interval was zero (impossible), the required
force would be infinite.

It seems that a work/energy solution might be more appropriate than a
force/mass solution, but even there, we would need to know something about
the behavior of the system at the point of impact.

Dick Baldwin

On Sun, Dec 18, 2011 at 11:14 PM, David Engebretson Jr. <
davide at soundandscience.com> wrote:

> Physics problem - have a solution?:
>
> Imagine a 68" object with a mass of 170 pounds travelling at 2.5 miles per
> hour (assume the mass is evenly distributed in the object in motion). The
> mass drops four feet and all of the momentum and other forces are placed in
> a single point on the object at 4 feet. Assume, also, that the bottom of
> the mass lands at the bottom of the four foot hole at the same time the
> impact upon the mass is inflicted upon the mass (ignore any loss of energy
> due to the landing of the mass in the bottome of the hole - the landing and
> the impact are ALMOST instantaneous).
>
> What is the amount of force that the mass absorbs at the time of impact?
>
> You can also assume the mass is 20" wide at the "point" of impact.
>
> In summary:
> The mass drops four feet travelling 2.5 mph. The impact area is 4 feet up
> from the bottom of the mass. The impact point is a single line 20" wide.
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--
Richard G. Baldwin (Dick Baldwin)
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http://www.DickBaldwin.com

Professor of Computer Information Technology
Austin Community College
(512) 223-4758
mailto:Baldwin at DickBaldwin.com
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