3. Peter ties a stone to the end of a thin string (1-meter long), and swings it with a period 2-seconds. The central acceleration of the stone is approximately (m/s²):
(A) 10
(B) 20
(C) 30
(D) 40
(E) 50
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統計: 尚無統計資料
統計: 尚無統計資料