A particle starts moving from time t = 0 and its coordinate is given as x(t) = 4t3 - 3t Choose the correct answer from the options given below :
- A, C, D Only
- A, B, C Only
- C, E Only
- A, C Only
Answer
(2) A, B, C Only
Solution
x = 4t3 - 3t v = dxdt = 12t2 - 3 a = dvdt = 24t
Turning point: v = 0 t2 = 14 t = 0.5
x(0.5) = 4(0.125) - 3(0.5) = 0.5 - 1.5 = -1, so the particle is 1 unit from the origin at its turning point. B correct, D incorrect.
Back at the origin: 4t3 - 3t = 0 t2 = 34 t = 32 = 0.866. A correct.
a = 24t 0 for t 0. C correct.
The particle does turn back (at t = 0.5), since its velocity changes from negative to positive. E incorrect.
A, B and C are correct.
Answer: (2)