Question

A car travels at 15 m/s for the first 20 s, 10 m/s for the next 30 s and finally 5 m/s for the next 10 s. Find its average speed.

Answer 1

Answer:

• Average speed of Car = 10.834 m/s

Explanation:

Car travels for first 15 seconds at 20 m/s

so,

[ using formula ;

distance = speed * time ]

→ distance covered in first interval, d₁ = 15 * 20

→ d₁ = 300 m

Then,

Car travelled for 30 seconds at 10 m/s

so,

→ distance covered in second interval, d₂ = 30 * 10

→ d₂ = 300 m

And,

Car travelled for 10 seconds at 5 m/s

so,

→ distance covered in third interval, d₃ = 10 * 5

→ d₃ = 50 m

Now,

Total time for which Car travelled = 20 s + 30 s + 10 s

Total time for which car travelled = 60 s

and,

Total distance covered by Car = d₁ + d₂ + d₃

Total distance covered by Car = 300 + 300 + 50

Total distance covered = 650 m

So,

→ Average speed = total distance covered / total time taken

→ Average speed = 650  / 60

→ Average speed = 10.834 m/s  

Therefore,

• Average speed of Car is 10.834 m/s.

Answer 2

Given:

• Car travels for 20sec with speed 15m/s
• Car travels for 30sec with speed 10m/s
• Car travels for 10 sec with speed 5m/s

━━━━━━━━━━━━━━━━━━

Need to find:

• Average speed =?

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Solution:

• Case 1

Speed= 15m/s

Time= 20sec

Then,

Distance = Speed× time

⟹ D1= 15× 20m

⟹$\purple{\bold{ D1= 300m}}$

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• Case 2

Time= 30sec

Speed= 10m/s

Then

Distance = Speed × Time

⟹ D2= 30×10 m

⟹$\purple{\bold{ D2= 300m}}$

━━━━━━━━━━━━━━━━

• Case3

Time = 10sec

Speed= 5m/sec

Distance = Speed× Time

⟹ D3= 10× 5m

⟹$\purple{\bold{ D3= 50m}}$

━━━━━━━━━━━━━━━━

■ Total distance travelled:

= D1 + D2 +D3

= 300m + 300m + 50m

=650m

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■ Total time taken to cover the total distance:

=20 sec+ 30 sec+ 10sec

= 60sec

━━━━━━━━━━━━━━━━

We know,

${Speed} _{avg} = \dfrac{total \: distance}{total \: time}m/s$

$\implies \: {Speed}_{avg} = \dfrac{650}{60} \: m/s$

$\red{\bold{ \implies \: {Speed}_{ avg} \: = 10.8333m/s}}$

▪Thus The average speed is 10.8333m/s