Answer:
B. positive; negative.
Explanation:
From the viewpoint of Principle of Energy Conservation and Work-Energy Theorem, we notice that gravity represents a conservative force, associated with gravitational potential energy, whereas air resistance is a non-conservative force, associated with dissipated work. Therefore, the work done by gravity is positive and work done by air resistance is negative. Therefore, the correct answer is B.
Answer:
-1.11 m/s²
Explanation:
v = at + v₀
Given v = 20 m/s, v₀ = 120 m/s, and t = 1.5 min = 90 s:
20 m/s = a (90 s) + 120 m/s
a = -1.11 m/s²