# IMG_20190307_110207.jpg Arrangement of two block system is as shown in the figure . mass of block A is â€¢m A 5K g and mass of B is 10Kg A constant force F = 100 N applied on upper block A . Friction between A and B is and b/w B and ground surface is smooth , then find work done by frictional force on block B in t = 2 sec if system starts from rest smooth

S safeer

For block A

N = mg    $f_K = \mu N$

=  $= \mu mg = \mu M_n g = 0.5 \times 5 \times 10 = 25 N$

For block B

$f_K = m_B a = \mu m_A g \\ a = \frac{\mu m_A g }{m_B } =$

$=\frac{ 0.5 \times 5 \times 10 }{10}= 2.5 m/s^2$

$s = \mu t + 1/2 at^2 \Rightarrow s = 1/2 \times 2.5 \times 4 = 5 m$

$W = F_k \times s \cos 0 = 25 \times 5 \times 1 = 125 J$

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