Question

the velocity of car is 72km/h after 10sec it stops calculate acceleration of car

Answer 1

Answer:
    Initial Velocity (u) = 72 km/hr = 72 * 1000 m/3600 s = 72*5/18m/s = 20 m/s
   Final Velocity (v)= 0
  time = 10 sec
 
we know that ,
           v = u +at
           0 = 20 +a*10
           -20 /10 = a
       or a= -2 m/s²

Hope this helps you!
Thank You!!
  Note :-
         1km = 1000 m
     and 1 hr = 60 minutes
       and 1 min = 60 seconds
 therefore , 1 hr = 60 *60 sec = 3600 seconds

and hence 1 km / hr = 1000 m / 3600 s = 5/18 m/s
     Just Remenber two Shortcuts :
                       km/hr = 5/18 m/s
         and        1 m/s = 18/5 km/hr

Answer 2

initial velocity =72 km/hr=20 m/s    time=10 sec
final velocity=0
v=u+at
0= 20+a*10
0=20+10a
-20/10=a
a=-2 m/s²