Ten one -rupee coins are put on top of each other on a table . Each coin has a mass m .
Give the magnitude and direction of
the reaction of the `6^(th)` coin on the `7^(th)` coin .

Explanation

The sixth coin is under the weight of four coins above it .
Reaction , r = - F = - m (kgf)
=-(4 mg)
Minus sign indicates that the reaction acts vertically upwards , opposite to the weight .