• # question_answer A constant retarding force of $80\text{ }N$is applied to      a body of mass $50\text{ }kg$which is moving initially      with a speed of$20\text{ }m/s$. What would be the time required by the body to come to rest?               A)  $15\,\,s$   B)  $14\,\,s$ C)  $12.5\,\,s$ D)  $1\,8\,\,s$

Here, $a=\frac{F}{m}=\frac{80}{50}=1.6m/{{s}^{2}}$ $u=20m/s$ and $v=0$ From    $v=u+at$ $0=20-1.6\times t$ $t=\frac{20}{16}=12.5\,s$