Question

Find the minimum horizontal force $\left(F\right)$ needed to start the slipping at any part of the system. (Take $g=10m/s^2$)

• A. $20\text{N}$
• B. $30\text{N}$
• C. $60\text{N}$
• D. $40\text{N}$

Answer 1

The correct option is C $60\text{N}$

First of all we need to check what is the friction available for all the three blocks.
For Block $\left(A\right)$:

$N_1=30g=300\text{N}$
$f_{\text{3 max}}=\mu N_1=\left(0.3\right)\left(300\right)=90\text{N}$

For Block $\left(B\right)$:


$N=40g=400\text{N}$
$f_{\text{2 max}}=\mu N=0.2\times 400=80\text{N}$

Similarly, for block $\left(C\right)$:


$N=60g=600\text{N}$
$f_{\text{1 max}}=\mu N=\left(0.1\right)\times 600=60\text{N}$

So, the minimum driving force required to start slipping at any point of the system is $60\text{N}$.