# physics

a car travels first half distance between two places with average speed of 30 km per hour and remaining half with a speed of 50 km per hour what is the average speed of the car is A 37.5KM/hr B 10km/hr //c// 42km/hr D 40km/hr

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1. let the distance be 200km

then
100km=30km/hr*t1 or t1=10/3 hr
and
100km=50km/hr*t2 or t2=2hr

avg speed= 200km/(16/3hr)=600/16=choice A

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2. d/2 = 30 t1 so t1 = d/60

d/2 = 50 t2 so t2 = d/100

t = t1 + t2

d = v (t1+t2) = v (d/60 + d/100)

100 = v ( 5/3 + 3/3) = (8/3) v

v = 300/8 = 37.5 km/hr

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posted by Damon

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