Q. The 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 $6^{th}$ (counted from the bottom) due to all the coins on its top is equal to $4\ mg$ (downwards)
B) The force on the $6^{th}$ coin due to $7^{th}$ coin is $4mg$ (downwards)
C) The reaction of the $6^{th}$ coin on the $7^{th}$ coin is $4\ mg$ (upwards)
D) The total force on the $10^{th}$ coin is $9\ mg$ (downwards)
Explanation
(d) [image:5_image229.emf]
(a) Is correct 6$^{th}$ coin has four coins on its top which exert a force $4mg$ on it
(b) Is correct. 7$^{th}$ coin has three coins, placed over it. Thus 7$^{th}$ coin exerts a force $4mg$ on 6$^{th}$ coin (downwards)
(c) Is correct. As what is explained in (b), the reaction of 6$^{th}$ coin on the 7$^{th}$ coin is $4mg$ (upwards)
(d) Is wrong 10$^{th}$ coin, which is the topmost coin, experiences a reaction force of $mg$ (upwards) from all the coins below it
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.