Question

A box of mass 20 kg is kept on a rough horizontal surface ($\mu =0.1$). There is a spring mass system having block of mass 20 kg and spring of spring constant 100 N/m in the box. There is no friction between block and box and spring is initially relaxed. Now, an external force of 120 N is applied on the box. Find the acceleration of the box (in $m/s^2$) just after applying the force.

Answer 1

Just after applying force;

force due to spring constant is;

$120-f_r=20a$

$120-\mu \left(2g\right)=20a$

$120-0.1\times 20\times 10=20a$

$120-20=20a$

$100=20a$

$a=5m/s^2$