How high would you have to go in the atmosphere for half of the mass of air to be below you?

Can you match these to the correct definition

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".

Bahan yang digunakan mencegah terjadinya polarisasi pada batu baterai a. larutan h2so4b. mncl2 dan serbuk karbonc. pbso4d. nh4cl