An interesting observation made by the firefighters was that some parts of the forest seemed to escape the flames. the crown fire would drop down into a ground fire in these areas, and then jump back up into the canopy as the fire burned into adjacent areas. they observed that many of these areas had previously been thinned, which means that some of the trees were cut down and hauled away to be used as timber. in other areas, thinned forests burned with as much severity as the unthinned forest. your objective is to design an observational study to answer the question: what was the determining factor for areas that escaped the worst impacts of the fire, compared to areas that were severely burned? select the best hypothesis and prediction that follow from the question you’re trying to answer. for getting started, see the hints.

Tom is having a problem with his washing machine. he notices that the machine vibrates violently at a frequency of 1500 rpm due to an unknown rotating unbalance. the machine is mounted on 4 springs each having a stiffness of 10 kn/m. tom wishes to add an undamped vibration absorber attached by a spring under the machine the machine working frequency ranges between 800 rpm to 2000 rpm and its total mass while loaded is assumed to be 80 kg. a) what should be the mass of the absorber added to the machine so that the natural frequency falls outside the working range? b) after a first trial of an absorber using a mass of 35 kg, the amplitude of the oscillation was found to be 10 cm. what is the value of the rotating unbalance? c) using me-3.5 kg. m, find the optimal absorber (by minimizing its mass). what would be the amplitude of the oscillation of the absorber?