Question

Block A is resting on floor and then it is pulled by a force F=2t (t= time), find time when block starts to slip on floor (take ${\mu }_s=\frac{1}{\sqrt{2}}$ ).

• A. 8 sec
• B. 12 sec
• C. 20 sec
• D. 15 sec

Answer 1

The correct option is D 15 sec

For Slipping to start $F_{net}(\text{parallel to surface)}\ge {\mu }_{s}N$ surface)

For slipping $Fcos{45}^o\ge {\mu }_{s}N$


given, ${\mu }_s=\frac{1}{\sqrt{2}}$

$\frac{F}{\text{/}\sqrt{2}}\ge \frac{1}{\text{/}\sqrt{2}}(mg-Fsin{45}^o)$

$F\ge mg-\frac{F}{\sqrt{2}}$

$F\ge \frac{mg}{(1+\frac{1}{\sqrt{2}})}$

$F\ge \frac{50}{1+0.7}$

So, $F\ge \frac{50}{1.7}$

$F\simeq 30$

2t=30

t=15 sec