Answer:
Average speed of the car = 16.53 m.s
Explanation:
For first 5 seconds:
As the car starts from rest, so the initial speed of the car, u=0
Acceleration, a= 4 m/s^2
So, the final speed (speed at time, t=5 second)
v=u+at
v=0 + 4 x 5 = 20 m/s
Distance covered,
s=50 m
As the car maintained the constant speed of 20 m/s for the next 10 seconds.
Distance traveled in 10 seconds, d=20 x 10 =200 m
For the last 4 seconds:
The car slows down at the rate of 2.0 m / s ^ 2 from the speed of 20 m/s.
As the car slows down, so the acceleration will be negative, i.e a=-2 m/s^2
s=80-16=64 m.
Considering all three cases, the total distance covered=
=50+200+64=314 m
Total time= 5+10+4=19 s
So, the averate peed= Totat distance covered / total time taken
=314/19=16.53 m/s