Question

On the horizontal surface of a truck a block of mass $1 \,kg$ is placed $(\mu = 0.6)$ and truck is moving with acceleration $5\, m/\sec^2$ then the frictional force on the block will be

• A. 5 N
• B. 6 N
• C. 5.88 N
• D. 8 N

Answer 1

Answer: (A)

$f_{rl}=\mu_sN=\mu_s\times mg=0.6\times1\times10=6 N.$
where $f_{rl}$ is the force of limiting friction.
Pseudo force $=ma = 1\times 5 ; F = 5\, N$
If $F < f_{rl}$, block does not move. So static friction is present.
Static friction = applied force .
$\therefore f_r=5\, N$.