Which of the following transitions will require the most thermal energy?
a)1 g of ice at –15 °c to 1 g of ice at –5 °c
b)1 g of ice at –5 °c to 1 g of water at 5 °c
c)1 g of water at 5 °c to 1 g of water at 15 °c
d)1 g of water at 15 °c to 1 g of water at 25 °c

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".