Question

In the situation shown in figure, $F=21N$. Find the magnitude of net external force acting upon the block A (all the surfaces are smooth)

• A. $21N$
• B. $14N$
• C. $7N$
• D. Zero

Answer 1

The correct option is C $7N$


Both blocks will move together
$F=ma$
$21=3\times a\Rightarrow a=7m/s^2$

$\Rightarrow T=1\times 7=7N$
Net external force on the block A = $7N$