Ten coins are placed on top of each other on a horizontal table. If the mass of each coin is 10gm, what is the magnitude and direction of the force on the 7th coin (counted from the bottom) due to all the coins above it? Take g=10m/s2
A
0.3 N downwards
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B
0.3 N upwards
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C
0.7 N downwards
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D
0.7 N upwards
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Solution
The correct option is A 0.3 N downwards The normal reaction that the 7th coin applies on 8th will balance the weight of 3 coins above it. Therefore, force from 3 coins above it will be, 3mg=3(10×10−3)(10)=0.3N (in downward direction)