Day 114 – Quantitative Energy


Physics 11 – Today we moved into more quantitative analysis of conservation of energy. I was pretty pleased with the previous class and the work done using bar graphs, and kids told me that they were feeling pretty good about. Gulp, that’s often a bad sign!

I could see today that several kids were not quite making the jump from bar graphs to using the conservation of energy equation.  Lots of the confusion stems from the students not knowing the beginning and end “situations.”  For example, consider the question below:

A 30.0kg gun is standing on a frictionless surface. The gun fires a 50.0g bullet with a muzzle velocity of 310m/s.  Calculate the kinetic energy of the bullet just after firing.

Several kids were very unsure of what the “beginning” and “end” are.  They were very used to have clearly drawn diagrams given to them.  This isn’t strange, research has shown that giving diagrams to students can actually impair their problem solving (I can’t find the reference just now, but I read it recently).

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