Question

When a $1700kg$ car skids to a stop with initial speed $9m/s$ on a flat road, it takes about $12m$ to stop. Given that friction is the force allowing the car to decelerate, how much distance would the same car need to stop if it were initially moving at $15m/s$?

• A. $33m$
• B. $48m$
• C. $20m$
• D. $15m$
• E. $18m$

Answer 1

Answer: (A)

$33m$

Given - $u=9m/s,v=0m/s,s_1=12m$

by $v^2=u^2-2as$ , where $a=$ deceleration ,

$0^2=9^2-2a\times 12$

or $a=81/24=27/8m/s^2$

now when $u=15m/s$

$0^2={15}^2-2\times 27/8\times s_2$

or $s_2=225\times 8/2\times \left(1/27\right)=33.3m$