#### Answer

0 m/s.
14 m/s.

#### Work Step by Step

Apply conservation of momentum.
a. In this case the two momentum vectors cancel. The total momentum is zero, and the wreckage after the collision doesn't move.
b. Refer to Figure 6.18. The total momentum is toward the northeast.
Each vector has length mv.
The momentum vectors are at right angles to each other. Find the magnitude of the combined momentum using the Pythagorean Theorem.
$$(20000 \frac{kg \cdot m}{s})^{2}+(20000 \frac{kg \cdot m}{s})^{2} =p^{2}$$
$$p=28284 \frac{kg \cdot m}{s} $$
The speed of the wreckage is this momentum divided by the total mass of the 2 cars, 2000 kg, which gives v = 14 m/s.