Question

水平轉(zhuǎn)盤上放一小木塊，當(dāng)轉(zhuǎn)速為60  r/min時(shí)，木塊離軸8 cm，并恰好與轉(zhuǎn)盤間無相對(duì)滑動(dòng)；當(dāng)轉(zhuǎn)速增加到120 r/min時(shí)，木塊應(yīng)放在離軸_______cm處才能剛好與轉(zhuǎn)盤保持相對(duì)靜止.

Answer 1

解析：木塊剛好保持與轉(zhuǎn)盤相對(duì)靜止時(shí)，它們間的最大靜摩擦力充當(dāng)其隨轉(zhuǎn)盤做勻速圓周運(yùn)動(dòng)的向心力，則

F_m=mω₁²r₁=mω₂²r₂                       ①

ω₁=2πn₁                                ②

ω₂=2πn₂                                ③

由①②③得

r₂=ω₁²r₁/ω₂²=n₁²r₁/n₂²

=(60/120)²×8  cm=2  cm.

答案：2