一质点作直线运动,某时刻的瞬时速度v=2m/s,瞬时加速度a=-2m/s2,则一秒钟后质点的速度是()
A. 等于零
B. 等于-2m/s
C. 等于2m/s
D. 不能确定
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一质点沿x方向运动,其加速度随时间的变化关系为a=3+2t (SI),如果初始时刻质点的速度v0为5m·s-1,则当t为3s时,质点的速度v=。
Question 1[音频]
A. She is going to have a lot of vanilla ice cream.
B. She won the spelling competition at her school.
C. She is going to the state capital for a competition.
D. She spelled "excellence" correctly, but others didn't.
Question 2[音频]
A. His family moved to Sacramento to settle down.
B. His family bought him a new suit and a new tie.
C. He went to Sacramento for a spelling competition.
D. He won the first prize in the state spelling competition.
Question 3[音频]
A. To make him feel better after he lost the first prize.
B. To apologize for not buying him some ice cream.
C. To wish him good luck in the next competition.
D. To congratulate him on winning the first prize.