AB is 1 / 4 circular arc track, radius r = 0.8m, BC is horizontal track, length s = 3M, friction coefficient at BC is u = 1 / 15, there are objects with mass m = 1kg AB is a 1 / 4 circular arc orbit with radius r = 0.8m, BC is a horizontal orbit with length s = 3M, and the friction coefficient at BC is u = 1 / 15. Now an object with mass m = 1kg slides down from point a to point C just stops. How much work does the resistance on the object in AB section of the orbit do?

The increment of total kinetic energy = 0
Work of gravity Mgr + work of resistance on circular orbit - umgs of overcoming resistance on horizontal orbit = 0
W=umgS-mgR=(1/15)*1*10*3-1*10*0.8=-6J
The minus sign indicates that the resistance in AB section of the orbit does negative work on the object, and the magnitude is 6J

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