1.

The motion of a particle along a straight line is described by equation : `x = 8 + 12 t - t^3` where `x` is in metre and `t` in second. The retardation of the particle when its velocity becomes zero is.A. `12 ms^-2`B. `24 ms^-2`C. zeroD. `6 ms^-2`

Answer» Correct Answer - A
`v = (dx)/(dt) = 12 - 3t^2 = 0`…(i)
If velocity is zero, `12 - 3t^2 = 0` which gives `t = 2 sec` For acceleration again differential equation (i)
`a = (d^2 x)/(dt^2) = - 6t` …(ii)
At time `t = 2 sec, a = -6 xx 2 = -12 m//s^2`
Hence retardation `= 12 m//s^2`.


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