Question

如圖所示,實(shí)線(xiàn)為電場(chǎng)中的電場(chǎng)線(xiàn),虛線(xiàn)為等勢(shì)面,相鄰等勢(shì)面間電勢(shì)差相等,一正電荷在等勢(shì)面A處時(shí)的動(dòng)能為20 J運(yùn)動(dòng)到等勢(shì)面C處時(shí)的動(dòng)能為零,現(xiàn)取B等勢(shì)面為零電勢(shì)能面,則當(dāng)此電荷的電勢(shì)能為2 J時(shí)動(dòng)能是(    )

A.2 J                              B.8 J

C.10 J                            D.18 J

Answer 1

B

解析：由動(dòng)能定理知,A→C過(guò)程克服電場(chǎng)力做功W_AC=ΔE_k=20 J,則A→B過(guò)程中克服電場(chǎng)力做功W_AB=W_AC=10 J，則在經(jīng)過(guò)B等勢(shì)面時(shí)，電荷的動(dòng)能E_kB=E_kA-W_AB=(20-10) J=10 J,A→B→C全過(guò)程中電荷的動(dòng)能與電勢(shì)能之和守恒,即保持10 J不變,故當(dāng)電荷電勢(shì)能為2 J時(shí),動(dòng)能為(10-2) J=8 J,B選項(xiàng)正確.