在用单摆测重力加速度的实验中同学在实验中，先测得摆线长为97.50cm，再测得摆球直径为2.00cm，然后测出了单摆全振动50次所用时间为98.0s，
（1）该单摆的摆长为 cm，周期为 s。
（2）如果他测得的g值偏小，可能原因是________
A．测摆线长时将摆线拉得过紧
B．误将摆线长当作摆长
C．开始计时，秒表按下偏迟
D．实验中误将49次全振动计为50次
(1) 98。50 1.96 (2) B
（1）根据题意可得周期为： t/n，由周期公式
得摆长为线长与半径之和（2）
所以g值偏小的原因可能是B对；
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