Question

Ten coins are placed on top of each other on a horizontal table. If the mass of each coin is $10$ gram and acceleration due to gravity is $10m{s}^{-2}$, what is the magnitude and direction of the force on the $7^{th}$ coin (counted from the bottom) due to all the coins above it? Neglect the force due to normal.

• A. $0.3N$ downwards
• B. $0.3N$ upwards
• C. $0.7N$ downwards
• D. $0.7N$ upwards

Answer 1

The correct option is A $0.3N$ downwards

Force on the seventh coin = weight of the three coins above it.

The mass of the above three coins (counted from the bottom) will be $30g=0.03kg$. Now the magnitude and direction of the force on the 7th coin (counted from the bottom) due to all the coins (three coins) above it $=0.03\times 10N=0.3N$

Direction of force will be downward.