4) a 56.9 kg slider descends an 8.21-meter high hill, encountering a friction force of 11.7 n.; the slider descends to a distance of 90m on the downhill.

e) none of the above answers are correct

in most common fires, oxygen is needed for an oxidation reaction to takes place. the combination of oxygen with any element as fuel can create fire and combustion will occur especially if wood, light materials and other combustible things are combine with oxygen.