Question

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 

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

1. There are 3 coins above the 7^th coin

Hence force = (3m) g

= 3mg N

2. The 8^th coin has two coins above it. Hence force exerted by 8^th coin on 7^th is, it’s weight plus the weight of two coins

= mg + 2 mg

= 3 mg N.

3. The 6th coin is under the weight of 4 coins above it

Reaction R = – F = – 4 mg N.