Question

The coefficient of friction between $4kg$ or $5kg$ blocks is $0.2$ and between $5kg$ block and ground is $0.1$ respectively. Choose the correct statements.(Take $g=10m/s^2$)

• A. Minimum force needed to cause system to move is $17N$
• B. When force is $4N$ static friction at all surfaces is $4N$ to keep system at rest
• C. Maximum acceleration of $4kg$ block is $2m/s^2$
• D. Slipping between $4kg$ blocks start when $F$ is $17N$

Answer 1

Answer: (C)

Maximum acceleration of $4kg$ block is $2m/s^2$

Friction force between $5kg$ block and ground is $f=0.1\times (5+4)\times 10=9N$
So, a minimum of $9N$ force is required to move the system and $4kg$ block starts when $F=9N$
From FBD of $4kg$ block, $4a=f=0.2\times 4\times 10=8,a=2m/s^2$
Thus,maximum acceleration of $4kg$ block is $2m/s^2$