Question

The brakes applied to a bike produce retardation of $5{\text{m/s}}^2$. If the bike takes $4\text{s}$ to stop after the application of brakes, calculate the distance it travels during this time.

• A. $40\text{m}$
• B. $45\text{m}$
• C. $35\text{m}$
• D. $50\text{m}$

Answer 1

The correct option is A $40\text{m}$

Given, $a=-5{\text{m/s}}^2,t=4\text{s}$ and $v=0\text{m/s}$
From first equation of motion, $v=u+at$
$0=u+(-5)\times 4$
$u=20\text{m/s}$
Distance being travelled, $s=ut+\frac{1}{2}a{t}^2$
$=20\times 4+\frac{1}{2}\times (-5)\times (4{)}^2$
$=80-40=40\text{m}$