which is has a greater momentum a cheetah with a mass of about 74 kg and a running speed of up to 31 m/s, or an elephant with a mass of 7000 kg running at 18 km/hr?

Guest Jul 29, 2014

Momentum is mass*velocity.

Cheetah: 74*31 = 2294 kg-m/s

Elephant 7000*18000/3600 = 35000 kg-m/s

Alan  Jul 29, 2014

momentum = mass x velocity


$$\dfrac{18km}{h} = \dfrac{18000m}{60*60sec}= 5m/sec$$


elephant momentum =   $${\mathtt{7\,000}}{\mathtt{\,\times\,}}{\mathtt{5}} = {\mathtt{35\,000}}$$      kg m/s


cheetah momentum = $${\mathtt{74}}{\mathtt{\,\times\,}}{\mathtt{31}} = {\mathtt{2\,294}}$$    kg m/s


So it appears that the elephant has more momentum

You beat me Alan  lol.

Melody  Jul 29, 2014

(Three is a charm!)


Similar to velocity, linear momentum is a vector quantity, possessing a magnitude and a direction.

This question does not require the use of a vector. The solution is the higher of the two products.

To solve this, first convert the speeds to the same units. Meters per second is the optimal choice.

$$Multiply \ $k/h by 0.2778 to approximate M/s.$$

$$\ 18 \frac{k}{h} \ * \ 0.2778 \ = \ 5 \ meters \ per \ second. \\\
\ 7000Kg \ * \ 5 \frac{m}{s} = 35000 \ Kg-m/s,\ for \ the \ elephant. \\\
74Kg * 31 \frac{m}{s} = 2294 \ Kg-m/s,\ for \ the \ cheetah. \\\$$


The elephant’s momentum is 15.26 times greater than the cheetah’s momentum.



DavidQD  Jul 29, 2014

Alternative question: What is the momentum generated by three forum members with a combined mass of "x" all moving at "y" meters per second to answer the same question???

Hint: It's definitely greater than the momentum of the cheetah and elephant combined!!!

Only answers converted to imperial minims will be accepted..........


CPhill  Jul 29, 2014

Well now, that might depend on which 3 forum members you are referring to.

There are 4 of us on at the moment but you could be talking about 3 of the children who are off having fun

I suppose if we were going fast enough it would not matter.  Perhaps that is really the question.  Find the minimum y value to make this statement true.    Umm   

Melody  Jul 29, 2014

Only answers converted to imperial minims will be accepted....

This is an interesting thought experiment.

I have a great affinity for imperial units of measure, especially imperial minims. I also have a great affinity for absurdly irrational units of measure, such as, light-years per fortnight, and Donkeypower. Twenty Mule Team cleaning power is in there, too.

One unit of measure I know you will appreciate: the Potrzebie. You are probably already familiar with it.

This thought experiment requires one more piece of information to answer in the desired units of imperial minims: a standardize tonic density of the “x” component.

If we figure that out, we might add to the list of humorous measurements.


I suppose if we were going fast enough it would not matter

Melody is correct, all we need to do is adjust the (Y) component of speed to compensate for any comparative values of the (X) component.

 Until next time. Live long and prosper!


DavidQD  Jul 29, 2014

AH.....the old "Potrzebie".......one of the most popular "units of measure" used in MAD magazine!!! (Actually, the Potrzebie can be defined in an infinite number of ways.......read all about it, here.....http://en.wikipedia.org/wiki/Potrzebie)

You would make The Hon. Alfred E  proud, DavidQD..........!!!!!

BTW......don't take the Potrzebie lightly.....WolframAlpha has "conversion" page dedicated to it.....http://www.wolframalpha.com/input/?i=potrzebie.......I see that their programmers must have a pretty good sense of humor.........!!!!



CPhill  Jul 29, 2014

... their programmers must have a pretty good sense of humor.

I agree. They do. Wolframalpha will answer how much wood, a woodchuck can chuck.

I’ve never tested a computer for its limits on humor. I suspect there is a measure for that, too. If not, we need to create one.



DavidQD  Jul 29, 2014

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