Question

A car travels at 72km/h for first 20s, 36 km/h for next 30s and finally 18 km/h for next 10s.
Find its average speed.

Answer 1

Given :-

A car travels at 72km/h for first 20s, 36 km/h for next 30s and finally 18 km/h for next 10s.

To Find :-

Average speed

Solution :-

We know that

1 km/h = 5/18 m/s

72 km/h = 72 × 5/18

72 km/h = 4 × 5

72 km/h = 20 m/s

36 km/h = 36 × 5/18

36 km/h = 2 × 5

36 km/h = 10 m/s

18 km/h = 18 × 5/18

18 km/h = 1 × 5

18 km/h = 5 m/s

Now,

◼ I n C a s e 1

Speed = 20 m/s

Time = 20 s

Distance = Speed × Time

Distance = 20 × 20

Distance = 400 m

◼ I n C a s e 2

Speed = 10 m/s

Time = 30 s

Distance = Speed × Time

Distance = 10 × 30

Distance = 300 m

◼ I n C a s e 3

Speed = 5 m/s

Time = 10 s

Distance = Speed × Time

Distance = 5 × 10

Distance = 50 m

Avg. Speed = Total distance/Total time

Avg. Speed = 400 + 300 + 50/20 + 30 + 10

Avg. Speed = 750/60

Avg. Speed = 75/6

Avg. Speed = 12.5 m/s

Answer 2

$\underline{\purple{\ddot{\Mathsdude}}}$

☆☆Answered by Rohith kumar maths dude ;-

72km/h=72×5/18==20m/s

36km/h = 36×5/18=10m/s

18km/h= 18×5/18=5m/s

☆☆In 1st case lets take ,

Speed= 20m/s

Time =20s

And,

Distance=speed×time

=20×20

=400m.

▪☆In second case,

Speed=10m/s

Time =30s

And,

Distance =speed ×time

=10×e0

=300m

☆☆In third case,

Speed =5m/s

Time=10s

And,

Distance= speed ×time

= 5×10

=50m.

☆☆Now total distance of i) ii) iii) cases:-

=400+300+50

=750

☆☆Total time=20+30+10=60

Now ,

Average speed= total distance/total time

=750/60

=12.5m/s

☆☆Hope it helps u mate .

☆☆Thank you