Ten one rupee coins are put on top of one another on a table. Each coin has a mass m kg. Give the
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.
1 Answers
(a) The force on 7th coin is due to weight of the three coins lying above it.
Therefore, F = (3 m) kgf = (3 mg) N
Where g is acceleration due to gravity. This force acts vertically downwards.
(b) The eighth coin is already under the weight of two coins above it and it has its own weight too. Hence force on 7th coin due to 8th coin is sum of the two forces i.e.
F = 2m + m = (3m) kg f = (3 mg) N
The force acts vertically downwards.
(c) The sixth coins is under the weight of four coins above it
Reaction, R = -F = -4 m (kgf) = - (4 mg) N
-ve sign indicates that reaction acts vertically upwards.