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Motion in A Straight Line question

2020 · 5 Sep · Shift 2 · Q39
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  5. /2020 · 5 Sep · Shift 2 · Q39

Motion in A Straight Line question

2020 · 5 Sep · Shift 2 · Q39

JEE MainPhysicsMotion in A Straight LineMCQ+4 / −1
The velocity (v) and time (t) graph of a body in a straight line motion is shown in the figure. The point S is at 4.333 seconds. The total distance covered by the body in 6 s is : JEE Main 2020 (Online) 5th September Evening Slot Physics - Motion in a Straight Line Question 80 English
  1. A
    12 m
  2. B
    11 m
  3. C
    494{{49} \over 4}449​ m
  4. D
    373{{37} \over 3}337​ m
View written solutionFree

Correct answer: D

  1. Key idea
    The total distance covered in a given time is the area under the speed–time graph.
    Since the graph given is a vvv–ttt graph, whenever velocity is negative, we must take its magnitude for distance.

  2. Reading the graph
    From the figure, the motion is piecewise linear and the marked point SSS occurs at t=4.333 s=133 s.t=4.333\text{ s}=\frac{13}{3}\text{ s}.t=4.333 s=313​ s.

    The graph consists of:

    • a positive triangular part from t=0t=0t=0 to t=2t=2t=2 s,
    • then a negative triangular/trapezoidal part from t=2t=2t=2 to t=133t=\frac{13}{3}t=313​ s,
    • then another negative triangular part from t=133t=\frac{13}{3}t=313​ to t=6t=6t=6 s.
  3. Distance from 000 to 222 s
    The first region is a triangle of base 222 s and height 2 m/s2\,\text{m/s}2m/s. d1=12×2×2=2 m.d_1=\frac{1}{2}\times 2\times 2=2\text{ m}.d1​=21​×2×2=2 m.

  4. Distance from 222 to 133\frac{13}{3}313​ s
    This region lies below the time axis, so we take positive area for distance.
    From the graph, this area comes out to d2=163 m.d_2=\frac{16}{3}\text{ m}.d2​=316​ m.

  5. Distance from 133\frac{13}{3}313​ to 666 s
    Again the graph is below the axis. The triangular area is d3=5 m.d_3=5\text{ m}.d3​=5 m.

  6. Total distance
    d=d1+d2+d3=2+163+5=7+163=21+163=373 m.d=d_1+d_2+d_3=2+\frac{16}{3}+5=7+\frac{16}{3}=\frac{21+16}{3}=\frac{37}{3}\text{ m}.d=d1​+d2​+d3​=2+316​+5=7+316​=321+16​=337​ m.

  7. Matching with options
    373 m\boxed{\frac{37}{3}\text{ m}}337​ m​ So the correct option is D.

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