Question

Ten one rupee coins are put on top of one another 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 coins above it.
(b) The force on the 7th coin by the eighth coin and
(c) The reaction of the sixth coin on the seventh coin.

CLASS - XI PHYSICS (Laws of Motion)

Answer 1

(a) no. of coins on 7th coin = 3
weight of 3 coins = 3mg
So force acting on 7th coin due to all coins above is 3mg.

(b) force acting on the eighth coin due to coins above it = 2mg
     The force acting on 7th coin will be the weight of 8th coin and the forces acting on it = mg+2mg= 3mg

(c)The normal reaction on 7th coin due to 6th coin is the same as the force acting on 6th coin due to 7th coin. 
force acting on the seventh coin due to coins above it = 3mg
The force acting on 6th coin will be the weight of 7th coin and the forces acting on it = mg+3mg= 4mg

Answer 2

(a) :--3mg

(b):--3mg

(c):--4mg.