A deadlift is a weightlifting exercise in which a weighted bar is raised straight up from the ground, pulled to the height of the weight lifter's hips, and then placed back on the ground. The world record for deadlifting is 500kg.
(a) How much work did the world record lifter do in raising the bar up to a height of 95 cm?
(b) How much work did he do while lowering the bar back to the ground?

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".