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A particle is moving in a straight line and its distance x from a fixed point on the line at any time t seconds is given by, x = t4/12 – 2t3/3 + 3t2/2 + t + 15. At what time is the velocity minimum?
  • a)
    1
  • b)
    2
  • c)
    3
  • d)
    4
Correct answer is option 'C'. Can you explain this answer?
Most Upvoted Answer
A particle is moving in a straight line and its distance x from a fixe...
Assume that the velocity of the particle at time t second is vcm/sec.
Then, v = dx/dt = 4t3/12 – 6t2/3 + 6t/2 + 1
So, v = dx/dt = t3/3 – 2t2/ + 3t + 1
Thus, dv/dt = t2 – 4t + 3
And d2v/dt2 = 2t – 4
For maximum and minimum value of v we have,
dv/dt = 0
Or t2 – 4t + 3 = 0
Or (t – 1)(t – 3) = 0
Thus, t – 1 = 0 i.e., t = 1 Or t – 3 = 0 i.e., t = 3
Now, [d2v/dt2]t = 3 = 2*3 – 4 = 2 > 0
Thus, v is minimum at t = 3.
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Community Answer
A particle is moving in a straight line and its distance x from a fixe...
Understanding the Problem
The position of the particle is given by the equation:
x = (t^4)/12 - (2t^3)/3 + (3t^2)/2 + t + 15.
To find the time at which the velocity is minimum, we first need to determine the velocity of the particle.
Finding Velocity
- The velocity (v) is the derivative of the position function (x) with respect to time (t).
So, we differentiate the position function:
v = dx/dt = (1/12)(4t^3) - (2/3)(3t^2) + (3/2)(2t) + 1.
This simplifies to:
v = (t^3)/3 - 2t^2 + 3t + 1.
Finding Minimum Velocity
- To find the minimum velocity, we need to set the first derivative of the velocity function (acceleration) to zero:
a = dv/dt.
This involves differentiating the velocity function:
a = (1/3)(3t^2) - 4t + 3.
This simplifies to:
a = t^2 - 4t + 3.
Next, we set this equal to zero to find critical points:
t^2 - 4t + 3 = 0.
Solving the Quadratic Equation
- Factoring gives:
(t - 3)(t - 1) = 0.
Thus, t = 1 and t = 3.
Determining Minimum Velocity
- We need to check the second derivative (d^2v/dt^2) or the nature of critical points to confirm which is a minimum:
- Testing intervals around t = 1 and t = 3 shows that at t = 3, the velocity is minimum.
Conclusion
- Therefore, the time at which the velocity is minimum is t = 3 seconds, confirming option C as the correct answer.
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