Question 5.29 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
(a) the force on the 7th coin (counted from the bottom) due to all the coins on its top,
(b) the force on the 7th coin by the eighth coin,
(c) the reaction of the 6th coin on the 7th coin.
Chapter Laws Of Motion Page 112
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(a) force on the 7th coin {counted from the bottom } = weight of coin above this
there are three coins above it.
so, weight of three coins = force on the 7th coin = 3*mg
= 3mg N
(b) force on the 7th coin by 8th coin
= weight of 8th coin + weight of coins above the 8th coins
there are two coins above the 8th coins
hence,
force on 7th coin by 8th coin = mg + 2*mg = 3mg N
(c) the reaction of 6th coin on the 7th coin = -( force exerted on 6th coin by above of it }
there are 4 coins above of 6th coin
hence,
the reaction of 6th coin on the 7th coin = -( weight of 4coins )
= - 4*mg N
= -4mg N
there are three coins above it.
so, weight of three coins = force on the 7th coin = 3*mg
= 3mg N
(b) force on the 7th coin by 8th coin
= weight of 8th coin + weight of coins above the 8th coins
there are two coins above the 8th coins
hence,
force on 7th coin by 8th coin = mg + 2*mg = 3mg N
(c) the reaction of 6th coin on the 7th coin = -( force exerted on 6th coin by above of it }
there are 4 coins above of 6th coin
hence,
the reaction of 6th coin on the 7th coin = -( weight of 4coins )
= - 4*mg N
= -4mg N
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