MTM Challenge

Unknown Mass Challenge

What was the challenge?

For this challenge, Will, Robert and I had to figure out the weight of a sack of salt without measuring it.  We were given a cart, a sack of salt, and a motion sensor to collect the velocity.  Here are the steps we took:

1) The empty cart's mass is 0.5kg.  Find the velocity of the empty cart by using Capstone and the motion sensors.  This will be your Va.

2) Put the sack of salt on top of the cart after finding the empty cart's velocity.  Find the full cart's velocity and record it.

3)By using the mava + mbvb = (ma + mb) (Vab) formula, solve for the salt's mass.

Data, Picture and Calculations

The empty cart's average velocity was 0.5 m/s, so here's how we solved for the momentum:

pemptycart = mv

pemptycart = (0.5) (0.57)

pemptycart = 0.28 kgm/s

We found the average velocity of the full cart to be slower, traveling at .24 m/s.  Once we obtained this information, we were able to solve for the mass of the sack of salt.

ptotalbefore = ptotalafter

mava + mbvb = (ma + mb) (Vab)

0.28 kgm/s + 0 = (0.28 + mb) (0.24)

0.28/0.24 = 0.28 + mb

1.16 = 0.28 + mb

0.89 kg = mb

We were very close to the actual weight.  We calculated that the salt's weight was 0.81 kg, but it was actually 0.77.  My thought is that we were a bit off on the velocity data collection, and for the future I would suggest that we do more trials to solve for the velocity, and then just take an average for an accurate collection of data.