Answer
a. B, A, C
b. C, B, A
c. C, B, A
Work Step by Step
a. Momentum is mv. Their momentum values, in the order ABC, are
$$(800 kg)(1.0 \frac{m}{s})=800 \frac{kg \cdot m}{s}$$
$$(1000 kg)(2.0 \frac{m}{s})=2000 \frac{kg \cdot m}{s}$$
$$(90 kg)(8.0 \frac{m}{s})=720 \frac{kg \cdot m}{s}$$
b. KE is $\frac{1}{2}mv^{2}$. Their KE amounts, in the order ABC, are
$$\frac{1}{2}(800 kg)(1.0 m/s)^{2} = 400 J$$
$$\frac{1}{2}(1000 kg)(2.0 m/s)^{2} = 2000 J$$
$$\frac{1}{2}(90 kg)(8.0 m/s)^{2} = 2880 J$$
c. The work needed to bring each object up to its respective speed from rest is the change in KE, or in this case, final KE - 0. The final kinetic energies were just calculated.