Question

An automobile travelling with a speed of 60km/hr, can brake to stop within a distance of 20m. if the car is going twice as fast, that is 120km/hr, the stopping distance will be

Answer 1

u= 60km/h =16.67 m/s
s=20m
v=0 (since the car stops)
therefore,v^2=u^2+2as
=0=(16.67)^2+2×a×20
=0=277.89+40a
=-(277.89)=40a
=a=277.89/40
=a=6.94m/s^2
now, u=120km/h=33.33m/s
a=6.94m/s^2, v=0
now,v^2=u^s+2as
=0=(33.3)^2+2×6.94×s
=-(33.3)^2=13.88s
=-1108.89=13.88s
=s=1108.89/13.88
=s=80m