Question

A cyclist, travelling at $15m/s$, applies brakes to avoid collision with a car $18m$ away. What deceleration must he have?

• A. $8.25m/s^2$
• B. $82.5m/s^2$
• C. $6.25m/s^2$
• D. $62.5m/s^2$

Answer 1

Answer: (C)

$6.25m/s^2$

In the given question
$u=15m/s$
$v=0m/s$ (As the the cycle finally stops)
$s=18m$
$a=?$
Using the third equation of motion,

$v^{{}^2}-u^2=2as{0}^2-{15}^2=2a\times 18-225=36aa=-\frac{225}{36}a=-6.25m/s^2$

Hence, the cyclist must have a deceleration of $6.25m/s$