Question

A 2 kg block is pressed against a rough wall by a force F= 20 N as shown in figure. Find acceleration of the block and force of friction acting on it. (Take g= $10m/s^2$).

• A. $12$ $m/s^2$, $4N$
• B. $14$ $m/s^2$, $12N$
• C. $4$ $m/s^2$, $12N$
• D. $4$ $m/s^2$, $2N$

Answer 1

Answer: (C)

$4$ $m/s^2$, $12N$

Force applied is $20N$

Normal reaction by wall is equal to force applied $20N$

friction force (static) = normal reaction X coff. of static friction

= 0.8X20

=$16N$ (upward)

friction force kinetic = normal reaction X coff. of kinetic friction

=0.6X20

=$12N$ (upward)

Motion of block is in downward direction due to gravitational force

acceleration of block is = $\frac{20-12}{2}$

= $4m{s}^{-2}$ (downward)