Question

The time taken by John , Raj and Abdul to reach their respective home varies. John reaches his house which is at a distance of 2km within 10 min. Raj reaches his home within 20 minutes by travelling 3km . Abdul travels 4km in 15 min and reaches his home .
i. Calculate their speeds
ii. Plot a distance- time graph in a graph sheet of their journey and compare the graphs

Answer 1

In this question Distance is constant .only speed and time varies. So in this type we use basic identity of formula of time and Distance keeping one identity which is distance constant.

S=D/T

S is indirectly proportion to T ( keep D constant)

Given data -

S1 = 2.5km /h

S2= 4.5km/h ( 2km increase speed so 2.5+2=4.5)

S1/S2= 2.5/4.5= 5/9

Therefore

T2/T1= 9/5 ( because S is indirectly proportion to T))

The reverse of speed is time taken

So T2 -T1 = 9–5 = 4unit

These 4unit = 16mint ( 16mint =6mint+10mint, time gap)

1unit = 4mint

So Time taken by T2 = 9unit = 9×4= 36mint ( convert 36mint into hour =36/60 hr )

So, Distance =speed ×time

Distance = 2.5Km/h × 36/60 hour = 1.5Km

Hope this unit method help you . With this method you can finish question in 5sec. Best of luck . Keep learning keep growing



hope this helps you