Question

The horizontal force required to drag a wooden cube of a side a on a rough horizontal surface is $F$. Another cube of the same wood but of side $2a$ is dragged on the same surface. Then the force required, if the cube is dragged with constant speed in both the cases, is:

• A. $F$
• B. $2F$
• C. $8F$
• D. $16F$

Answer 1

The correct option is C $8F$

$m=\rho \times v$
$m_1=\rho (a{)}^3$ and $m_2=\rho (2a{)}^3=8\rho a^3$
$\Rightarrow m_2=8m_1$
$\Rightarrow$ normal reaction increased by 8 times

therefore, friction force also increses by 8 times.

And, as the block is moving with constant velocity, thus $a=0$

thus, $F=$ friction force
$\therefore$ F increases by 8 times.