Question

场强e=10^4n/c的水平匀强电场中,有一根长l=15cm的绝缘细线,一端固定在o点,

Answer 1

在细线水平时,如从o点到小球的联线与E同向,小球释放后电场力做负功,与E反向时电场力做正功.

重力的功Wg=mgL=0.003kg*10N/kg*0.15m=0.0045J

电场力做功的大小=QEL=2*10^-6*10^4*0.15=0.003J

细线对小球不做功

动能定理,在小球由释放到B奌时,合外力的功=动能增量=0.5mV^2=0.0015V^2

电场力做负功时,0.0015V^2=0.0045-0.003=0.0015,V=1m/s

电场力做正功时,0.0015V^2=0.0045+0.003=0.0075,V=2.236m/s