Question

Ten one-rupee coins are put on top of each other on a table. Each coin has a mass m. Which of the following statements is not true?

• A. The force on the $6^{th}$ coin (counted from the bottom) due to all the coins on its top is equal to 4mg (downwards).
• B. The force on the $6^{th}$ coin due to the $7^{th}$ coin is 4mg (downwards).
• C. The reaction of the $6^{th}$ coin on the $7^{th}$ coin is 4 mg (upwwards).
• D. The total force on the ${10}^{th}$ coin is 9mg (downwards).

Answer 1

The correct option is B The force on the $6^{th}$ coin due to the $7^{th}$ coin is 4mg (downwards).

As per Newtons third law of motion, the 6th coin will produce an equal reaction force on the 7th coin, but in the opposite direction. Hence, the reaction force of the 6th coin on the 7th coin is of magnitude 4mg. This force acts in the upward direction.