W合=△Ek
WA+WB(B做负功)=1/2m(V^2-0)+(1/2)*4m(V^2-0) 因为不计摩擦,所以VA=VB=V
FaSa*cos(90-30)+(-1)FbSb=5/2m(V^2-0)=5/2mV^2
4mgS*cos60-mgs=5/2mV^2
V^2=(2/5)gs
细线断后,B做竖直上抛运动,所以W合=△Ek
mgH-mgs=1/2m(V^2-0)=6/5mgs
H=6/5s=1.2s
W合=△Ek
WA+WB(B做负功)=1/2m(V^2-0)+(1/2)*4m(V^2-0) 因为不计摩擦,所以VA=VB=V
FaSa*cos(90-30)+(-1)FbSb=5/2m(V^2-0)=5/2mV^2
4mgS*cos60-mgs=5/2mV^2
V^2=(2/5)gs
细线断后,B做竖直上抛运动,所以W合=△Ek
mgH-mgs=1/2m(V^2-0)=6/5mgs
H=6/5s=1.2s