) A. Car A doesn't have to go east. B. car b must drive west. C. car c may be heading west. D. The directions of the three cars may be the same solution: D Hint: People on the C car see the trees on the roadside moving west, which means that the C car is moving east. People in the car see car C moving westward relative to car A, which means that both car A and car C are moving eastward, and car A is moving faster than car C. The movement of car B is uncertain, and it may be moving eastward, westward or stationary. So choose D.
A regular stone with the aspect ratio of 1:2:4 is placed on the horizontal ground. What is the ratio of its maximum pressure to its minimum pressure?
Solution: According to the pressure formulas P = f/s and F = g, the ratio of the minimum stress area to the maximum stress area on the ground is 2: 8.
So P 1:P2
=F 1/S 1:F2/S2
=F 1/S 1*S2/F2
=F 1/F2*S2/S 1
=G 1/G2*S2/S 1
= 1/ 1*8/2=4/ 1
That is, the ratio of the maximum pressure to the minimum pressure on the ground is 4: 1.