Question

For relative motion to be there between two blocks, the minimum value of F should be:

• A. 15 N
• B. 30 N
• C. 25 N
• D. 32 N

Answer 1

The correct option is B 30 N

Let the force at which motion b/w the blocks

just begins be F

Acc. of system at force $F=\frac{F-5}{5}m/s^2=a$

At this state, limiting static friction will

acting at the upper contact surface (i.e)

$F_1=F_{limit}=M_{s}mg=0.5\times 3\times 10$

$=15N$

Applying $F_{net}=ma,$

$F-f_1=ma$

$\Rightarrow F-15=3\left(\frac{f-5}{5}\right)$

$\Rightarrow 2F=75-15$

$\Rightarrow F=30N\left(B\right)$