A driver of a car travelling at 52 km h^-1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 seconds. Another driver going at 3 km h^-1 in another car applies his brakes slowly and stops in 10 seconds. 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?
Question is from Science Book class 9 CBSE page 112
Please answer this question properly
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Answers
Answer:
Initial speed of the car A u=52 kmh
−1
=52×
18
5
=14.44 ms
−1
The car stops in 5 seconds i.e v=0 at t=5
(A) : Initial speed of the car A u=3 kmh
−1
=3×
18
5
=0.83 ms
−1
The car stops in 10 seconds i.e v=0 at t=10
With the help of these initial and final points for both the cases, we can plot the graph of speed vs time.
Area under the speed-time graph gives the distance covered.
∴ Distance covered by car A x
A
=
2
1
×14.44×5=36.1 m
∴ Distance covered by car A x
B
=
2
1
×0.83×10=4.15 m
Answer:
As given in the figure below PQ and SQ are the speed-time graph for given two cars with initial speed 52 kmh¹ and 3 km ¹
Distance travelled by first car before coming to rest = Area of rectangle OPR
=1 ×5s ×52kmh¹
2
= 1 ×5 (52 × 1000/60×60)
2
= 1 × 5 ×130
2 9
= 36.11m
Distance travelled by 2nd car before coming to rest = Area of rectangle OSQ
= 1 ×OQ× Os
2
=1 ×10×(3×1000/60×60)
2
=5×5
6
=25
6
=4.16m