Question

A car of mass 1200 kg moving with a speed of 54 km per hour stops after travelling a distance of 60 M retarding uniformly the work done by brake force is .....

Answer 1

╭╼╾╼╾╼╾╼╾╼╾╼╾╼╾╮
┃ ┈┈ [_Hɪ Mᴀᴛᴇ_] ┈┈┈ ┃
╰╼╾╼╾╼╾╼╾╼╾╼╾╼╾╯

$\mathfrak{\underline {Solution \: :}}$

mass of the car,m = 1200kg
Initial velocity,u = 54km/h =>54*5/18 =>15 m/s
Final velocity,v=0 m/s
distance,s=60 m

We know that,
v² - u² = 2as

a = v² - u² /2a

a = (0 - 15² ) / 2*60

a= -225/120

a= -1.875 m/s²

Retardation = 1.875 m/s²

$\bold{Force\: applied \:by\: the\: brakes}$
=>Force retardation,F =
mass * retardation
=60*-1.875
$\bold{= -112.5 N}$ [Ans.]

Work done = Force * displacement
=-112.5 * 60m
=-6750 J

°•°1 J = 1/1000 KJ

•°•6750J=6.75 KJ

Answer - $\bold{-6.75\: KJ}$