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JEE Main 20246 AprilMorning Shift
Exam
JEE Main
Year
2024
Date
6 April
Shift
Morning Shift
Subject
Physics
Chapter
Motion in One Dimension

JEE Main 2024 · 6 April · Morning Shift · Physics · Motion in One Dimension

A train starting from rest first accelerates uniformly up to a...

A train starting from rest first accelerates uniformly up to a speed of 80 km/h80 \mathrm{~km} / \mathrm{h} for time tt, then it moves with a constant speed for time 3t3 t. The average speed of the train for this duration of journey will be (in km/h\mathrm{km} / \mathrm{h} ) :

Options

  1. A40
  2. B80
  3. C30
  4. D70

Correct answer

D. 70

Step-by-step solution

 Average speed = total distance  time taken =80×t2+80×3t4t=70km/hr.\begin{aligned} \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} .\end{aligned}
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