Question

A wooden block of weight 20 N is pushed along a rough horizontal surface at constant speed by a horizontal force of 10 N. Which of the following is the coefficient of static friction between the block and the surface? $({\mu }_s>{\mu }_k)$

• A. Zero
• B. Less than 0.5
• C. Equal to 0.5
• D. Greater than 0.5

Answer 1

The correct option is D Greater than 0.5

Let,
W is the weight of the block, F is force on block.
As per the problem,
$W=mg=20N$............(1)
$N=mg=20N$..............(2)
where, variables have their usual meanings.
As it is moving with constant speed means zero acceleration.

$W=F$
$F={\mu }_{k}N$
$10={\mu }_k\left(20\right)$
${\mu }_k=0.5$
Therefore, As the block is moving which implies it has overcome this frictional force giving us the coefficient of friction as ${\mu }_s>0.5$