- Home
- Standard 11
- Physics
4-2.Friction
hard
A force $F=t$ is applied to block $A$ as shown in figure. The force is applied at $t=0$ seconds when the system was at rest and string is just straight without tension. Which of the following graphs gives the friction force between $B$ and horizontal surface as a function a time $' t '.$
A
B
C
D
Solution
$F-f_{r_A}=0 \Rightarrow t-\mu_s m g=0 \Rightarrow t=\mu_s m g$$\text { [till or } f_{r B}=\mu_s m g$
$t-\mu_s m g=\mu_s m g$
$\left.t=2 \mu_s m g\right]$
$T=F-f_{r A}=f_{r B}$
$T=t-\mu_s m g=f_{t B}$
$t=\mu_s m g \text { block be will not move }$
$\mu_s m g$
$\text { static friction will work }$
$\text { after } t > 2 \mu_s m g \text { kinetic friction will work }$
$a =\frac{ F -\mu_{ s } mg -\mu_{ k } mg }{ m }$
$a =\frac{ F -\mu_{ s } mg -\mu_{ k } m g}{ m }$
So $\quad T=F-\mu_s m g-m a \quad$ after $t=2 \mu_s m g$
Standard 11
Physics
