The object with mass m = 20 kg moves in a straight line along the horizontal plane under the action of constant horizontal external force F In 2S, f is opposite to the direction of motion, and in 4S, f is the same as the direction of motion, (g = 10m / S ^ 2). Calculate the dynamic friction coefficient between the object and the horizontal plane. (0s: v = 10m / S; 2S: v = 0; 4S: v = - 2m / s)

The object with mass m = 20 kg moves in a straight line along the horizontal plane under the action of constant horizontal external force F In 2S, f is opposite to the direction of motion, and in 4S, f is the same as the direction of motion, (g = 10m / S ^ 2). Calculate the dynamic friction coefficient between the object and the horizontal plane. (0s: v = 10m / S; 2S: v = 0; 4S: v = - 2m / s)

The solution of 0-2s VT = V0 at is a = 5m / S ^ 2
2-4s VT = V0 + a't solution gives a '= 1m / S ^ 2
And F + F = ma
F-f = ma 'is replaced by F = 3M and F = 2m
When u = f / Mg, u = 0.2