Physical change: by cutting the three it went to small logs. This is a change of shape and size, which didn't chaghe the chemical consitutution (molecules). It still is made of the same compounds of the original three. That is why this is a physical change.
Chemical change: By firing the logs the organic matter went into a combustion reaction, which is a chemical change: Organic matter + O2 at hight temperature -> CO2(g) + CO(g) + H2O(g).
