(1)a1=v1/t1=(2m/s)/4s=0.5m/s^2(2)h=1/2(a1)(t1)^2+v1*t2+1/2(a2)(t3)^2=(1/2*0.5*16+2*9+1/2*0.5*16)m=26m(3)15s末,加速度a2=0.5m/s^2方向竖直向下,FN=m(g-a2)=570N
1.a=2/4=0.5m/s^22.分三段解3.用加速度算