Question

Find the frictional force between the two blocks. Take $g=10{\text{m/s}}^2$.

• A. $20\text{N}$
• B. $72\text{N}$
• C. $80\text{N}$
• D. $100\text{N}$

Answer 1

The correct option is A $20\text{N}$

By F.B.D,
$N_1=12\text{g}$
$f_{\text{max}}=\mu N_1=72\text{N}$



Assume them to move together with common acceleration $a_c=\frac{F}{m_1+m_2}=\frac{50}{20}=2.5{\text{m/s}}^2$
For them to move together, required friction force
$f=8a_c=20\text{N}$.
But $f<f_{\text{max}}$, hence the frictional force $f=20\text{N}$.