Question

b) 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. Find its average speed.
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Answer 1

Answer:

$\frac{65}{6}$ m/s

Explanation:

Car travels at 54 km/h for 20 s

In m/s

54×5/18=15 m/s

We know that

Distance=speed×time

=36×20=300m

For next it travel 36 km/h for 30 s

In m/s

36×5/18=10m/s

Distance=10×30

=300m

finally 18km/h for 10 s

In m/s

18×5/18=5m/s

Distance=5×10

=50m

$average \: speed = \frac{total \: disatance}{total \: time}$

$\frac{300 + 300 + 50}{20 + 30 + 10}$

$\frac{65}{6}$

Thus,Average speed=$\frac{65}{6}$m/s

Answer 2

Given :-

The car travels at 54 km/h for 1st 20 seconds

36 km/h for next 30 seconds

18 kh/h for next 10 seconds.

To Find :-

Average speed of the car

Solution :-

Average speed = Total distance travelled by car / Total Time Taken by car to covered that distance

Therefore,

54 × 5 /18 = 15 m/s

Similarly with other distance also

36 × 5/18 = 10 m/s

And 18 × 5/18 = 5 m/s

In the given case,

A car travels 54 km/h for first 20 seconds

We known speed = distance / time

distance = speed × time

= 15 × 20

= 300 m

Similarity with other also

We get,

300 m & 50 m

Total distance travelled = 300 + 300 + 50 m = 600 + 50 = 650 m

Total Time Taken = 20 + 30 + 18 = 60

Average speed = 650 / 60

= 65 / 6 m/s