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:

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

(b) the force on the 7th coin by the eighth coin,

(c) the reaction of the 6th coin on the 7th coin.

Answer 1

(a) The seventh coin will experience force equal to the sum of weights of the three coins above it. As each coin is of m kg, therefore, force on seventh coin = 3 m kgf = mg N.

(b) The eighth coin supports the weights of two coins above it. Therefore, the force on seventh coin due to the eight coin will be equal to the sum of the weights of the eighth coin and the two coins above it. Therefore, force on seventh coin due to eighth coin = m + 2m = 3m kgf = 3 mg N.

(c) The sixth coin experiences force equal to weight of the four coins above it. Hence, reaction due to sixth coin on the seventh coin = 4 m kgf = 4 mg N.