Question

(b)A driver of a car travelling at 72km/h applies the brakes and accelerates
uniformly in the opposite direction. The car stops in 5 s. Another driver
going at 18km/h 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?
​

Answer 1

Answer:

(A) : 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

Thus car A travels more distance than B.

solution

Answer 2

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