A driver of a car travelling at 52 km h I applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h-l in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
Answers
"From the given data,
For first car:
Initial velocity, u = 52 km/h
Let's convert km/h into m/s
u = 52 km/h = 52×1000/3600 = 14.4 m/s
Final velocity, v = 0 km/h = 0 m/s
Time, t = 5 s
For second car:
Initial velocity, u = 3 km/h
Let's convert km/h into m/s
u = 3 km/h = 3×1000/3600 = 0.83 m/s
Final velocity, v = 0 km/h = 0 m/s
Time, t = 10 s
Let's draw a speed-time graph
Img 45_18
Hence, Distance travelled by the first car = Area of the triangle AOB
AOB = ½ × OB × AO
= ½ × 5 × 14.4
AOB = 36.1 m
Similarly, Distance travelled by the second car = Area of the triangle COD
COD = ½ × OD × CO
= ½ × 10 × 0.83
COD = 4.1 m
Therefore, the second car travels 4.1 m and first car travels 36 m, before coming to rest.
From the above data,
It is clear second car travelled farther after the barkers were applied."