Three blocks of masses 6 kg, 4 kg and 2 kg are pulled on a rough surface by applying a constant force 20 N. The values of coefficient of friction between blocks and suface are shown in figure.
Q. Friction force on 6 kg block is

Options

A. 9.2
B. 7.8
C. 4
D. 9.8

Answer

B

Explanation

The system of masses is shown below
From the figure
`F - T_(2) = ma`
and `T_(1) - T_(2) = ma`
equation (I gives,
`10.2 - T_(1) = 2 xx 0.6` `implies` `T_(1) = 10.2 - 1.2 = 9N`
Again from equation (ii), we get `9 -T_(2) = 2 xx 0.6` `implies` `T_(2) = 9 - 1.2 = 7.8 N`