Question

A car travel 10 km distance at a speed of 60km/h and returns with a speed of 40km/h . calculate its average speed for the whole journey.

Answer 1

A bus travels a distance of 10 km with a speed of 60 km/h.

Given that, distance (d) = 10 km and speed of bus (s) = 60 km/hr.

Also given that, the bus returns with a speed of 40 km/h.

Still, the distance is the same i.e. 10 km.

Assume that the bus starts from point A to B (A→B) and covers a distance of 10 km with a speed of 60 km/hr.

Now, the bus returns to it's actual point A (from B to A point) with a speed of 40 km/hr.

So, the total distance covered= (A→B + B←A) 10 + 10 = 20 km

We know that,

Average velocity is defined as total distance covered by the total time taken.

Also time = distance/speed

According to question,

→ 20/(10/60 + 10/40)

→ 20/(0.16 + 0.25)

→ 20/(0.41)

→ 48.78 km/hr

Answer 2

Given :-

• Car Travel 10km at a speed of 60km/h.
• Return at Speed of 40km/h.

To Find :-

• Average Speed for whole journey ?

Solution :-

→ Speed of Car while going forward = 60km/h

→ Distance covered = 10km.

→ Time taken = (Distance / speed) = (10/60) = (1/6) Hours.

Now,

→ Speed of Car while going Returning = 40km/h

→ Distance covered = 10km.

→ Time taken = (Distance / speed) = (10/40) = (1/4) Hours.

So,

→ Total Distance Covered by car = 10 + 10 = 20km.

→ Total Time taken = (1/4) + (1/6) = (3+2)/12 = (5/12) hours.

So,

→ Average Speed = (Total Distance) / (Total Time)

→ Average Speed = (20) /(5/12) = 20 * (12/5) = 48km/h.

Hence, Average Speed of Car for the whole journey is 48km/h.

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Direct Formula :-

☛ Average Speed = ( 2 * S₁ * S₂ ) / (S₁ + S₂)

Here, we Have :-

➼ S₁ = 60km/h.

➼ S₂ = 40km/h.

So,

☞ Average Speed = (2 * 60 * 40) / (60 + 40)

☞ Average Speed = (2 * 60 * 40) / (100)

☞ Average Speed = 48km/h.

Hence, Average Speed of Car for the whole journey is 48km/h.

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