5. Find the average speed, if a cyclist travels,
(i) 6 km/h for 25 minutes and 8 km/h for
15 minutes.
(ii) 5 kilometres up a hill at 16 km/h and
back down at 24 km/h.
Answers
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Step-by-step explanation:
speed = distance/time
distance = speed × time
i) t1 = 25 mins = 25÷60 hrs = 5/12 hrs
distance d1 = 6/(5÷12) = 12×6/5 =72/5 = 14.4km
t2 = 15 minutes = 15÷60 =1/4 hrs
distance d2 = 8/ (1/4) = 8×4 =32 km
total distance = d1+d2 = 14.4+32 = 46.4 km
total time = t1+t2 = 5/12 +1/4 = 5+ 3/12 = 8/12 = 2/3 hrs
average speed = total distance/ total time
= 46.4/(2/3) = 69.6 hrs
ii) average speed = 2ab/a+b
a= 16 kmph, b = 24 kmph
average speed = 2×16× 24/ (16+24)
= 2×16×24/40 =19.2 kmph
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