Question

Two blocks of mass $8kg$ and $4kg$ are connected a heavy string placed on through horizontal plane, The $4$kg block is pulled with a constant force $F$. The co-efficient of friction between the blocks and the ground is $0.5$. What is their value if $F$ so that the tension in the spring is constant through out during the motion of the blocks ? $(g=10m{s}^{-2})$

• A. $40N$
• B. $60N$
• C. $50N$
• D. $30N$

Answer 1

The correct option is B $60N$

Given mass $m_1$=8 kg,thus normal force$N_1$=8$\times$10=80 N

mass$m_2$=4 kg, thus normal force$N_2$=4$\times$10=40 N

Now frictional force for on object 1 $f_1=N\mu$=80$\times$0.5=40 N

and frictional force for on object 1 $f_2=N\mu$=40$\times$0.5=20 N

Thus total frictional force$f_1+f_2$=60 N