Question

A car is travelling at 72 kilometer per hour . When brakes are applied it experiences a uniform acceleration of 2 meter per second.How long does it take the car to stop? How far does it travel from the instant brakes are applied

Answer 1

72 kmph =72(5/18)=20
v=u+at
0=20=(-2)t
0=20-2t
2t=20
t=20/2=10sec
s=ut+0.5at^2
s=20(10)+0.5(-2)(10^2)
s=200-100
s=100m
The car travels 100m before it stops and it takes 10sec to stop





















10)

Answer 2

u = 72 kmph = 72 * 5/18 = 20 m/s
a = - 2 m /s²
v = 0

the equation of motion in single dimension is :
       v = u + a t
       0 = 20 - 2 * t
    t = 10 seconds.
 
  s = u t + 1/2 a t²
     = 20 * 10 - 1/2 * 2 * 10²
     = 100 meters.

  OR,    v² = u²  + 2 a s
           s = ( 0²  - 20² ) / -2 * 2
               = 100 meters