Question

a car travels at 54km/hr for first 20s 36 km/hr for next 30s and finally 18km per hr for next 10s .find its average speed

Answer 1

hi friend,

average speed=total distance/total time


distance travelled during first 20s is speed ×time

v1=54kmph×5/18=15m/s

distance= 15(20)=300m

distance travelled in next 30s is speed ×time


v2=36kmph×5/18=10m/s

distance = 10(30)=300


distance travelled in the next 10s is speed ×time

v3=18kmph×5/18=5m/s

distance =(5)(10)=50m


average speed =300+300+50/60

=650/60m/s


I hope this will help u :)

Answer 2

Hi there !!

First case :-
Speed = 54 km/hr = 54 x 5/18 = 15 m/s

Time taken = t₁ = 20 sec

distance = speed x time
= 15 x 20 = 300 metres


--------------------------------

Second Case :-
speed = 36 km/hr = 36 x 5/18 = 10 m/s

Time taken = 30 sec

distance = speed x time
= 10 x 30 = 300 metre
----------------------------------------

Third Case:-

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

Time taken = t₃ = 10 sec

distance = speed x time
= 5 x 10
= 50 metre

------------------------------------------------------------------

Total distance covered = 300 + 300 + 50
= 650 metres

Total time taken = 20 + 10 + 30 = 60 sec

Average speed = Total distance covered / Total time taken
= 650 / 60
= 10.83 m/s [ approx.]