    Question

# A car moving on a straight road covers first 1000 s of its journey with speed of 18 km/h and next 2000 s of its journey with speed of 36 km/h. Average speed of the car during whole journey is

A
18 km/h
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B
36 km/h
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C
27 km/h
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D
30 km/h
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Solution

## The correct option is D 30 km/hGiven data: V1=18 km/h, t1=1000 s ⇒t1=1000/3600 h V2=36 km/h, t2=2000 s ⇒t2=2000/3600 h Assume the distance covered in two steps be d1 and d2. Average speed: V=total distanetotal time V=d1+d2t1+t2 V=V1.t1+V2.t2t1+t2 V=18×10003600+36×2000360010003600+20003600 V=5+205/6=6×5=30 km/h Alternate Method: If you divide the total time travel into equal intervals, such that you know the speed in each interval, you can use the formula for average speed. V=V1+V2+V3+....+Vnn ⇒V=V1+V2+V33 V=18+36+363=903=30 km/h  Suggest Corrections  0      Similar questions  Related Videos   Speed and Velocity
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