# Thread: Weighing of unknown masses

1. Hi
I was recently faced with the question: " How would you get the mass of two unknown objects without using a scale or density?". This has been eating away at me and I was hoping that someone would be able to help me

2.

3. are you allowed to use a rope, tie each end to one of the masses and hang that over a somehow frictionless pole or pulley. then with the acceleration of the bigger one (m1) down you could get the an equation for the masses ( 9.8 : a = [m1 - m2] : m1) ... then on a frictionless surface throw one at a certain speed straight at the other, then measure the velocities of both after. Then with the momentum must stay the same in collisions rule figure out an equation something like (m1)(v1i) = p = (m1)(v1f) + (m2)(V2f). Then if you had that I'm pretty sure you have enough equations to get the mass of both masses... or maybe not and I'm crazy, whchever works...

4. It really sound like something that might work but once again there is a problem thet i'm faced with... How will i determine the velocities of the two objects?

5. set up a tripod with a video camera on top and record the collision, then since the framerate is usually 32 frames per second (I think) you can use that to get the velocities.

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