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 :
- (a) a=-5 α v⁵
- (b) a=-3 α v²
- (c) a=-2 α v³
- (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.
- 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
- 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.
- Solve for a. So -a/v² = 2α v. Multiplying both sides by -v² gives a = -2α v³.
- 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.