Question

An automobile starts from rest and accelerate uniformly for 30sec to speed of 72kmh-¹.then it moves with a uniform velocity and it is finally brought to rest in 50m with a constant retardation. If the total distance traveled is 950m,find the acceleration,retardation and total time taken.

Answer 1

Part A (Acceleration)
u=0m/s
v=72 km/h =( 5/18)*(72) = 20m/s
t=30 sec
v=u+at
20=0+ a*30
a=20/30
a=2/3 m/s2
distance covered
s=ut+1/2at2
s=0+(1/3)*(30*30)
s=300m

Part C(retardation)
u=20m/s
v=0
s=50
v2 - u2=2as
0-(20*20)=2*a*50
a= -400/100
a= -4m/s2
v=u+at
0=20+(- 4)*t
t=5sec

Part B (Uniform motion)
s= 950-50-300
s=600 m
t=600/20
t=30sec

#so total time taken is = 30 + 30 + 5=65sec