多谢多谢想了半小时终于依着答案的数字a=4F/3M弄出来了，
答案说a=4F/3M，所以根据答案，应该有一个与F方向相同的摩擦力，设为f，
于是质心加速度为(F+f)/M （待求），圆筒的角加速度应该等于质心加速度，也是(F+f)/M
再以圆筒与地面接触点为转轴，列出torque的方程式：F×2R=(1/2*MR^2+MR^2)×(F+f)/M =====> f=F/3
所以a=(F+f)/M=4F/3M
只是还是不知道为什么这个地面的摩擦力是和F同向的？
Because F does not act on the com of the object.
When F is some distance away from the COM, it is intuitive that the cylindrical object tends to rotate about its axis. However, in the real-world, the cylinder rolls on the surface under F, which means there is another force in the same direction of F that forces the center of the cylinder to move. That's f.
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