Calculate Mass Without Scale - Using Cars & Momentum

[elitespart]

If you were give an uknown mass and told to find it's mass w/out using a scale, how would u go about doing it. You have a meter stick, stopwatch, and 2 cars (which you can mass) w/ flat surfaces so you can put the unknown weight on it. I want to use the conservation of momentum in elastic collisions to figure out the unknown mass, but how would I go about incorprating the friction into it? any other info. would also be very helpful. Thanks.

 

[berkeman]

Since you know weight (and therefore the mass) of the cars, just make your own balance with the meter stick. Use the stopwatch as the fulcrum, and put one car on one side and the unknown mass on the other side. Use the relative distances when balanced to tell you the unknown mass.

That was easy.