Verified Solution • 2025–26 Session moderate

QJEEM19Ph123e: JEE Main 2019 Physics - Class 11 JEEM19Ph123e Solution: The time dependence of the position of a particle of mass m = 2 …

The time dependence of the position of a particle of mass m = 2 is given by r→(t)=2ti^−3t2j^\overrightarrow r \left( t \right) = 2t\widehat i - 3{t^2}\widehat j . Its angular momentum, with respect to the origin, at time t = 2 is

Multiple Choice Options

  • A 36 k^\widehat k
  • B - 48 k^\widehat k
  • C −34(k^−i^)- 34\left( {\widehat k - \widehat i} \right)
  • D 48(i^+j^)48\left( {\widehat i + \widehat j} \right)

Step-by-Step Verified Solution

v→=2i^−6+j^\overrightarrow v = 2\widehat i - 6 + \widehat j

At t = 2
v→=2i^−12j^\overrightarrow v = 2\widehat i - 12\widehat j

P→=mv→=4i−24j^\overrightarrow P = m\overrightarrow v = 4i - 24\widehat j

At t = 2
r→=4i^−12j^\overrightarrow r = 4\widehat i - 12\widehat j

L→=r→×P→=|i^j^k^4−1204−240|

={4(−2)+4×12}k^= \left\{ {4( - 2) + 4 \times 12} \right\}\widehat k

=(−96+48)k^= \left( { - 96 + 48} \right)\widehat k

=(−)48k^= \left( - \right)48\widehat k

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