Question

Find the friction force (in $\text{N}$) between the blocks in the figure (Assume ground to be smooth)

• A. 5.0
• B. 5
• C. 5.00

Answer 1

Answer: (A), (B), (C)

FBD is

Limiting friction between blocks is
$f_{max}=\mu N_1=0.3\times 20=6\text{N}$
To start sliding between blocks, limiting friction has to be attained
$f_{max}=2\left(\frac{F}{6}\right)=6\Rightarrow F=18\text{N}$
Given that.
$F=15\text{N}$
Hence, both blocks move together with $a=\frac{F}{6}=\frac{5}{2}{\text{m/s}}^2$
$\Rightarrow f=2a=2\times \frac{5}{2}=5\text{N}$