JEE Main 2024 · 31 January · morning · Single correct · +4 / −1

The relation between time 't' and distance 'x' is t=α x²+β x, where α and β are constants. The relation between acceleration (a) and velocity (v) is :

  1. (a) a=-5 α v⁵
  2. (b) a=-3 α v²
  3. (c) a=-2 α v³
  4. (d) a=-4 α v⁴
Answer and solution

Answer (c) a=-2 α v³

Solution

Physics sir · 4 steps

Differentiate t with respect to x to get 1/v, then differentiate once more with respect to time.

  1. Get 1/v. Since t is given as a function of x, differentiate with respect to x. This gives dt/dx = 2α x + β, and dt/dx is just 1/v.

    1/v = 2α x + β

  2. Differentiate in time. Differentiate both sides with respect to t. The left side gives -1/v²dv/dt = -a/v². The right side gives 2αdx/dt = 2α v, and β drops out.
  3. Solve for a. So -a/v² = 2α v. Multiplying both sides by -v² gives a = -2α v³.
  4. So. The relation is a = -2α v³, which is option (c).

The idea to keep. When time is given as a function of position, dt/dx = 1/v. Differentiating 1/v in time gives -a/v², so the acceleration appears directly.

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 2024.