JEE Main 2021 · 18 March · morning · Single correct · +4 / −1

The position, velocity and acceleration of a particle moving with a constant acceleration can be represented by :

  1. (a)
    Option (a)
  2. (b)
    Option (b)
  3. (c)
    Option (c)
  4. (d)
    Option (d)
Answer and solution

Answer (b)

Solution

Physics sir · 3 steps

Constant a makes v a straight line, and a straight-line v makes x a parabola. Check each panel for that.

  1. Build the chain. With constant a, the velocity is v = u + at, a straight line of slope a. The position is x = x₀ + ut + 1/2at², a parabola.
  2. Slopes must agree. The slope of the x–t graph is v, and the slope of the v–t graph is a. A positive constant a means v rises steadily, so the x curve keeps getting steeper and bends upward.
    Optionx–tv–tFits constant a > 0?
    (a)straight linecurve getting steeperNo: a curved v means a changes, and a straight x means v is constant
    (b)parabola bending upwardstraight line risingYes
    (c)straight linestraight line risingNo: a straight x means v is constant, yet v is rising
    (d)curve bending upwardstraight line fallingNo: a falling v needs a < 0, but a is drawn positive
  3. So. Only (b) has a constant a, a straight-line v and a parabolic x, so the answer is (b).

The idea to keep. Each graph is the slope of the one before it. Constant a gives a straight-line v and a parabolic x. Check that each slope matches the next graph.

Answer from the NTA final answer key. Solution by PrepWiser.

Study Rectilinear Motion

Asked about 110 times in JEE Main since 2020. This question is from 2021.