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 force on the `7^(th)` coin (counted from the bottom ) due to all the coins on its top

Explanation

The eighth coin is already under the weight of two coins above it and it has its own weight too . Hence force on 7th coin due to 8th coin is sum of the two forces i.e,
F=2m+m=(3 m)kgf=(3 mg)N
The force acts vertically downwards .