Question

Ten one rupee coins are put on top of each other on a table. Each coin has a mass m kg. Give the magnitude and direction of

1. the force on the 7^th coin (counted from the bottom) due to all the coins on its top
2. the force on the 7^th coin by the 8^th coin
3. the reaction of the 6^th coin on the 7^th coin.

Answer 1

$$\begin{gathered} Lettherearennumberofcoins. \\ 1.theforceon{7}^{th}coindueallcoinsaboveitonthetop=\left(n-7\right)mg=\left(10-7\right)mg=3mg,directionis \\ verticallydownwards. \\ 2.theforceon{7}^{th}coindueto{8}^{th}coin=forceofthecoinsabove{8}^{th}coin+forceof{8}^{th}coin \\ =\left(n-7\right)mg=\left(10-7\right)mg=3mg.Thedirectionisverticallydowdwards. \\ 3.Thereactionof{6}^{th}coinon{7}^{th}coinisF=\left(n-6\right)mg=\left(10-6\right)mg=4mganditisverticallyupwards. \end{gathered}$$