设木板厚度为D,木板对子弹的摩擦阻力为f
设所求速度为V1
(1/2)mV^2=fD
(1/2)mV^2-(1/2)mV1^2=f(D/2)=(1/2)fD=(1/4)mV^2
(1/2)V1^2=(1/2)V^2-(1/4)V^2=(1/4)V^2
V=V/(根号2)=(根号2)V/2
选D
设木板厚度为D,木板对子弹的摩擦阻力为f
设所求速度为V1
(1/2)mV^2=fD
(1/2)mV^2-(1/2)mV1^2=f(D/2)=(1/2)fD=(1/4)mV^2
(1/2)V1^2=(1/2)V^2-(1/4)V^2=(1/4)V^2
V=V/(根号2)=(根号2)V/2
选D