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A particle moving in a straight line covers a distance of x cm in t second, where x = t^3 + 6t^2 – 15t + 18. What will be the velocity of the particle at the end of 2 seconds?(a) 20cm/sec(b) 22cm/sec(c) 21cm/sec(d) 23cm/secThis question was posed to me in class test.Query is from Application of Derivative in division Application of Derivatives of Mathematics – Class 12

Answer» CORRECT OPTION is (c) 21cm/sec

The explanation is: We have, x = t^3 + 6t^2 – 15t + 18

Let, V be the velocity of the particle at the END of t SECONDS. Then,

v = dx/dt = d/dt(t^3 + 6t^2 – 15t + 18)

So, v = 3t^2 + 12t – 15

Thus, velocity of the particle at the end of 2 seconds is,

[dx/dt]t = 2 = 3(2)^2 + 12(2) – 15 = 21cm/sec.


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