Question

a boy walks to his school at a distance of 6 kilometres with a constant speed 2.5 kilometre per hour and walk back with a constant speed of 4 kilometre per hour find the average speed ​

Answer 1

GiveN :

• A boy goes to his school which is at a distance of 6 km.
• Speed of boy, while going to school $\rm{v_1 \: = \: 2.5 \: kmh^{-1}}$
• Speed of boy while coming from school $\rm{v_2 \: = \: 4 \: kmh^{-1}}$

To FinD :

• Average speed of boy

SolutioN :

Use formula for the average speed, in case when object moves equal distance is different time intervals.

$\large \implies {\boxed{\rm{v_{avg} = \dfrac{2(v_1 v_2)}{v_1 + v_2}}}}$

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$\implies \rm{v_{avg} = \dfrac{2(2.5 \times 4)}{2.5 + 4}}$

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$\implies \rm{v_{avg} = \dfrac{2(10)}{6.5}}$

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$\implies \rm{v_{avg} = \dfrac{20}{6.5}}$

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$\implies \rm{v_{avg} = 3.076}$

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$\implies \rm{v_{avg} \approx 3.1}$

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$\small \underline{\rm{\therefore \: Average \: velocity \: of \: boy \: is \: 3.1 \: kmh^{-1} \: (approx.)}}$

___________________________

• Speed is rate of change of Distance travelled.

• SI unit of speed is m/s.

• Speed is a scalar quantity.

• $\sf{Average\ Speed = \dfrac{Total\ Distance}{Total\ Time}}$

Answer 2

Going from home to school-

Constant speed = 2.5km/h

Distance = 6km

Time taken = 6/2.5

= 2.4 hours

$\rule{200}{2}$

Going from school to home-

Constant speed = 4km/h

Distance = 6km

Time taken = 6/4

= 1.5 hours

$\rule{200}{2}$

Total time is taken in traveling = 3.9 hours

Total distance = 12km

Average speed of round-trip = 12/3.9

= 3.08 hours

$\rule{200}{2}$