JEE MAIN - Physics (2024 - 1st February Morning Shift - No. 24)

A particle is moving in one dimension (along $x$ axis) under the action of a variable force. It's initial position was $16 \mathrm{~m}$ right of origin. The variation of its position $(x)$ with time $(t)$ is given as $x=-3 t^3+18 t^2+16 t$, where $x$ is in $\mathrm{m}$ and $\mathrm{t}$ is in $\mathrm{s}$.

The velocity of the particle when its acceleration becomes zero is _________ $\mathrm{m} / \mathrm{s}$.
Answer
52

Explanation

  • Position (x): The particle's location on the x-axis at a given time.

  • Velocity (v): The rate of change of position with respect to time

( $v = \frac{dx}{dt}$ ).

  • Acceleration (a): The rate of change of velocity with respect to time

( $a = \frac{dv}{dt}$ ).

The particle's position is given by:

$$x(t) = -3t^3 + 18t^2 + 16t$$

We need to find the velocity when the acceleration is zero.

  1. Find the Velocity (v) and Acceleration (a) Functions:

  • Velocity:

$$v(t) = \frac{dx}{dt} = -9t^2 + 36t + 16$$

  • Acceleration:

$$a(t) = \frac{dv}{dt} = -18t + 36$$

  1. Find the Time (t) When Acceleration is Zero:

$$a(t) = 0$$

$$-18t + 36 = 0$$

$$t = 2 \text{ seconds}$$

  1. Calculate the Velocity at t = 2 seconds:

$$v(2) = -9(2)^2 + 36(2) + 16$$

$$v(2) = 52 \text{ m/s}$$

Answer:

The velocity of the particle when its acceleration becomes zero is 52 m/s.

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