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Motion In Straight Line

Question
CBSEENPH11026198

A particle moves along a straight line OX. At a time t (in second) the distance x ( in metre ) of the particle from O is given by x = 40 + 12 t - t3 . How long would the particle travel before coming to rest?

  • 24 m

  • 40 m

  • 56 m

  • 16 m

Solution

C.

56 m

Speed is rate of change of distance.

Distance travelled by the particle is

               x = 40 + 12 t - t3

We know the speed is rate of change of distance

       i.e       ν = dxdt

                  ν = ddt40 + 12t - t3

                     = 0 + 12 - 3t2

but final velocity ν = 0

∴               12 - 3t2 = 0

⇒               t2 = 123   t2 = 4

 ⇒              t = 2s

Hence, distance travelled by the particle before coming to rest is given by
             x = 40 + 12(2)-(2)3

             x = 64 - 8

              x = 56 m