Ten coins each of mass m are placed one over . . .

Question : Ten coins each of mass m are placed one over other. Force exerted on 4th coin from bottom by third coin from bottom is 

a) 4 mg

b) 6 mg

c) 7 mg

d)  None of the above.

Doubt by Muskan

Solution : 

Force exerted on the 4th coin from the bottom by the third coin will be equal to normal reaction of 3rd coin. 

The normal reaction of 3rd coin will be equal to weight of the 7 coin above it i.e. 7 mg

so, c) would be the correct option.