Question

3. Two cars A and B start a journey of 100 km at
the same point of time. Car A travels with a
uniform speed 40 km/h. Car B travels with 60
km/h speed, but stops after half an hour for 15
minutes due to engine failure. When it restarts
its speed remains 50 km/h. For the journey:
(1) Draw the speed-time curve.
(ii) Find out which car will finish the journey
first and how much time earlier?
[Ans. Car B, 21 minute early]
[68]​

Answer 1

Answer:

car B will finish 21minutes earlier

Explanation:

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Answer 2

Answer:

CarA:

Sa = 40km/h, D = 100km

Ta = 100/40 = 2.5 hrs

CarB:

Sb1 = 60km/h, T1 = 0.5 hrs

Db1 = 60 * 0.5 = 30km

Remaining dist. = 100 - 30 = 70km

Time wasted due to failure =  T2 = 15min = 1/4 hr

T3 = 70/50 = 7/5 hr = 84min

Tb = T1 + T2 + T3 = 30min + 15min + 84min = 129min

Tb = 129min

Ta = 2.5hrs = 150min

So, Car B reaches first by 21 mins.

For the Speed-time graph, Car A will be a straight line

For Car B It will be straight with speed 60km/h until 30mins, after that drop the curve to 0 and after 45 mins again draw straight line with speed being 50km/h