Solve these problems:

A. Which of the equations below for position, x, as a function of time, t, is surely wrong?

1. x(t) = 2 m - (5 m/s²)t²
2. x(t) = 2 m + (2 m/s)t - (5 m/s²)t²
3. x(t) =-(2 m/s³)t² - (2 m/s³)t³
4. x(t) =-(2 m/s)t - (2 m/s³)t³
5. x(t) = 2m cos(t/(2s))

B. Which of the following cases represents the position of a particle which is approaching the origin at t=0?

1. x(t) = 2 m - (5 m/s²)t²
2. x(t) = 2 m + (2 m/s)t - (5 m/s²)t²
3. x(t) =-2m - (2 m/s)t - (2 m/s²)t² - (2 m/s³)t³
4. x(t) = 3m - (2 m/s)t - (2 m/s³)t³
5. x(t) = 2m cos(t/(2s))

For problems (3)-(5) You must show a correct method as well as a correct answer for full credit.

C. A rock is shot out of a cannon straight upward on the Moon. After it is shot and before it crashes back down its acceleration is the constant acceleration of gravity on the Moon, 1.6 m/s² downward, its initial speed is 480 m/s and its initial height is 1.4 m.

1. What is the greatest height that the rock reaches?
2. When does it reach that height?

D. A 98.0 kg professor has stepped onto a floor with wet wax on it. Only two forces act on him: a force of gravity equal to -961 N k and a force, F_f, due to the floor. His position, r, as a function of time is given by r(t) = (1.00 m/s) t k . Find F_f .

E. In a color TV picture tube an electric field exerts a net force of

-1.60 X 10^-13 N i on a positron, whose mass 9.11 X 10^-28 g. What is the positron's acceleration?