本题目来源于试卷: 美国2021年物理杯赛真题 PHYSICS BOWL 2021，类别为 美国物理杯赛(Physics Bowl)
[单选题]
At t=0, Ball 1 is rolling up a ramp and Ball 2 isreleased from the top of the same ramp. The ballsdon’t collide. Which velocity vs. time graph at rightbest represents the motion of the two balls? 
A. A
B. B
C. C
D. D
E. Both A & D
参考答案: A
本题详细解析:
Ball 1 starts with a positive velocity and is rolling on the same ramp as Ball 2, therefore,
they have the same acceleration (slope of v-t graph).
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