Question

A car travels at 54 km/hr for first 20 sec. , 36 km/hr for next 30 sec. and finally 18 km/hr for next 10 seconds. Find its average speed ?​

Answer 1

Answer:

54 km/hr = 54 x 5/18 = 15 m/s

36 km/hr = 36 x 5/18 = 10 m/s

18 km/hr = 18 x 5/18 = 5 m/s

1st Case  

Speed = 15m/s

Time = 20 s

Distance = Speed x Time = 15 x 20 = 300 m

2nd Case

Speed = 10 m/s

Time = 30 sec

Distance = 10 x 30 = 300 m

3rd Case  

Speed = 5 m/s

Time = 10s

Distance = 5 x 10 = 50 m

Now Total Distance = 300 + 300 + 50 = 650 m

Total time = 20 + 30 + 10 = 60 s

Average Speed = 650/60 = 65/6 m/s

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Answer 2

GiVEN :-

• A car travels at 54 km/h for first 20 s, 36 km/h for next 30 s and finally 18 km/h for next 10 s.

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TO FiND :-

• The average speed of the car.

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FORMULA USED :-

• x km/h = x × (5/18) m/s
• Distance = Speed × Time
• Average speed = Total distance covered/Total time taken

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SOLUTiON :-

For first 20 s,

• Speed = 54 km/h = 15 m/s
• Time = 20 s

Distance = Speed × time

• ⇒Distance = 15 × 20
• ⇒Distance = 300 m

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For next 30 s,

• Speed = 36 km/h = 10 m/s
• Time = 30 s

Distance = Speed × time

• ⇒Distance = 10 × 30
• ⇒Distance = 300 m

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For next 10 s,

• Speed = 18 km/h = 5 m/s
• Time = 10 s

Distance = Speed × time

• ⇒Distance = 5 × 10
• ⇒Distance = 50 m

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• Total distance covered = 300 + 300 + 50 = 650 m
• Total time taken = 20 + 30 + 10 = 60 s

• Average speed = 650/60
• Average speed = 10.8 m/s

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