Question

A block of $10Kg$ is placed on a rough horizontal surface whose cofficient of static friction ${\mu }_s$ is equal to $0.5$. A force of $100N$ is exerted on the block as shown in the figure. The minimum force that must be applied on the block vertically downwards so that the block doesn't move is

• A. $100N$
• B. $150N$
• C. $200N$
• D. $225N$

Answer 1

Answer: (A)

$100N$

$m=10kg$

Since the friction is a self-adjusting force and it remains between $0$ and the maximum frictional force,

So, $0\le f_s\le \mu N$

$100\le 0.5N$
$100\le 0.5[100+F]$
$200\le 100+F$

$F\ge 100N$
$\therefore$ Minimum F $=$ 100 N