The first stage: slow down to the left at a constant speed, which can be obtained from Newton's second law, μ g = Ma, a=2? m/s2
t 1=v0a=3s，x 1=v02t 1=9m。
The second stage: accelerate to the right at a uniform speed until the speed is equal to that of the conveyor belt;
t2=va=2s，x2=v？ 2t2=4m。
The third stage: T3 = x 1? x2v= 1.25s。
Total time t=t 1+t2+t3=6.25? s
A: It takes 6.25 s for an object to start moving and return to its starting point.