A train starting from rest first accelerates uniformly up to a speed of 80 mathrm{~km} / mathrm{h} f

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2.Motion in Straight Line

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A train starting from rest first accelerates uniformly up to a speed of $80 \mathrm{~km} / \mathrm{h}$ for time $t$, then it moves with a constant speed for time 3t. The average speed of the train for this duration of journey will be (in $\mathrm{km} / \mathrm{h}$ ) :

A

$80$

B

$70$

C

$30$

D

$40$

(JEE MAIN-2024)

Solution

$\text { Average speed }=\frac{\text { total distance }}{\text { time taken }}$

$=\frac{\frac{80 \times \mathrm{t}}{2}+80 \times 3 \mathrm{t}}{4 \mathrm{t}}=70 \mathrm{~km} / \mathrm{hr}.$

Standard 11

Physics

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