Which of the following is an idea that robert hutchings goddard introduced in his “further developments” to his research "a method of reaching extreme altitudes"?
a. lunar energy
b. nuclear energy
c. solar energy
d. wave energy

Air flows upward in the wick of a lantern because of the liquid property called

Gordon is going for a run through the park, but it is cold outside. the low outside temperature could affect his personal safety.

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".