Question

If mass of $A=10kg$, coefficient of static friction ${\mu }_s=0.2$, coefficient of kinetic friction ${\mu }_k=0.2$ and the mass of $B\text{is}20kg$. Then find the acceleration of the masses.

• A. $6m/s^2$
• B. $7m/s^2$
• C. $8m/s^2$
• D. $9m/s^2$

Answer 1

The correct option is A $6m/s^2$

The FBDs of the masses are as shown

From the FBD we have
$N=10g=100\text{N}$
$f={\mu }_{k}N=\left(0.2\right)\left(100\right)=20\text{N}$

Hence, acceleration of the system is given by
$a=\frac{\left(\text{Supporting Force - opposing Force}\right)}{\text{Total mass}}$
$=\frac{20g-f}{30}=\frac{200-20}{30}$
$=6m/s^2$